CR 0 creatures are not likely to be much use in combat, but they will still have some uses for scouting, blending in, or utility. A few special mentions:
Almiraj (ToA): Although an affront to evolution and aesthetics both, the lowly almiraj does sport advantage on most Perception checks, as well as decent stealth. In an area where they occur, uh, ‘naturally’, you could use one as a scouting form.
Badger: Burrow speed.
Cat: A common sight in many places, which makes it a useful spying form. It also has climb speed.
Crab: Amphibious and sporting a swim speed. Also has blindsight.
Cranium rat (VGtM): Not much use for conjuring, but wild shaping into one for the Telepathic Shroud could come in handy. Immunity to divination spells is a powerful tool to have in your box, though only sporadically needed. Telepathy is also useful in overcoming language barriers, and of course lets you communicate with your party freely while in this shape.
Deer: Fastest ground speeds at this tier, though not as fast as the CR ¼ Riding Horse.
Flying Monkey (ToA): Since it can fly, you won’t be able to wild shape into this until level 8, by which time there seems less reason to use this. By that time, an owl is still a good, nimble and unobtrusive scout. But a monkey does have little hands, allowing it to manipulate things like door handles, so maybe if you need to enter a home, or rifle through some papers? Of course, you will attract more than a little attention if you use this shape in an area where they aren’t normally found.
Frog: Amphibious and a swim speed. Also has darkvision.
Hyena: Like the deer, it has the fastest ground speeds at this tier, though not as fast as the CR ¼ Riding Horse.
Owl: Excellent flyer, including flyby to avoid opportunity attacks, darkvision, keen senses and a fast flight speed.
Tressym (SKT p. 242): Fly and climb speeds, detect invisibility and poison. As a winged cat, they draw rather a lot of attention, which is generally bad.
CR 1/8 beasts are generally lacking in combat prowess, but are less vulnerable than CR 0. Two worth pointing out:
Flying Snake: Extremely versatile creature with both fly and swim speeds, blindsight, flyby to avoid opportunity attacks and even a respectable damage capability for the tier, coupled with very good aim.
Giant Crab: Like its smaller cousin, this crab sports blindsight, swim speed and it is amphibious. Its defences are also noteworthy, with better native AC than you’ll find in CR 1/4. With its grappling claws, it is a possible combat form if you like control better than damage, despite the CR.
In the
CR 1/4 tier, we find the first combat forms of most druids. A small swarm of eight of these creatures can be summoned with Conjure Animals and a third level spell slot. Some standouts:
Cow (VGtM): Low AC and slightly elevated hp for the tier, the lowly cow is str 18 on a Large frame (540 lb carrying capacity), and it charges so you can feel it. Considered a Huge frame if it's an Ox variant (for a whopping 1080 lb carrying capacity).
Rothé are smaller and slightly less durable underdark cows with flashing lights and infravision. And Stench Kows have resistances to three damage types and a stench aura that can poison those nearby. A straight upgrade over the basic cow.
Dimetrodon (ToA, VGtM): One to one comparison with the CR ¼ wolf has the dimetrodon come out on top. They have considerably more hp and deal more damage. In packs, the wolves are more useful with their special abilities (pack tactics and trip). So this one is best used for fairly specific circumstances, where each summon must fight pretty much alone, and should last a while – such as a series of small tunnels.
Draft Horse: If you need muscle and can apply it with the equine form, here’s strength 18 on a large animal (carrying capacity 540 lbs) for you, with a brisk movement rate. At a pinch, this beast can defend itself, with its decent hp and damage. It has AC 10, however.
Compared to the cow above, the draft horse is faster and has a few more hp, making it generally less vulnerable, but it lacks the cow’s charge. It beats the cow for damage in a slugging match, though.
Giant Badger: The basic damage dealer of the tier, but not particularly resilient. Sports burrowing and darkvision.
Giant Bat: Since they are size large, the DM may let the party use them as mounts, in which case they make an interesting option. If summoned by a lvl 6+ Shepherd, they have 30hp a piece, which is pretty impressive for the tier. They have echolocation, and get advantage on Perception for hearing.
Giant Poisonous Snake: If you’re up against enemies not resistant to poison (whether directly or via good con save), this is the most hard-hitting slugger of the tier. It has poor hp but the best AC you’ll see outside giant crabs and ankylosaurs. It even has a bit of blindsight.
Giant Wolf Spider: Spider climb and web senses, and an impressive +7 Stealth. 10' blindsight and 60' darkvision. Not a straightforward combat form, being rather squishy, but it has it uses.
Hadrosaurus (ToA, VGtM): Large. Conjuring these would probably be in order to take advantage of the mobile wall of scales and meat it gets you. Between their size and considerable hp pool, they can fill up a battlefield and make it hard or impossible for the enemy to manoeuvre. And they’ll deal non-negligible damage while they’re at it.
Hadrosaurs have AC 11 compared to cow and draft horse AC of 10, and at least equivalent hp. The draft horse kicks slightly harder than the hadrosaurus can bash, but is particularly more precise. This means for slugging matches, the horse beats the dino most of the time.
Panther: A fast animal with fine climb speed, but its punch is poor in toe-to-toe slugging and if its pounce fails to come off in charges. As usual for large cats, it has expertise in Stealth for a total of +6.
Riding Horse: The fastest land speed you are likely to find. Turn into one or conjure a bunch for mounts for your party. Feel free to run them ragged.
Velociraptor (ToA, VGtM): Tiny. Comes close to a straight upgrade over the CR ¼ wolf, and could be your standard conjured beast for this tier if they exist in the campaign world. The raptor’s size allows four of them to attack from the space occupied by one wolf (though the front row may give the target cover from the second row). This allows them to better concentrate attacks, and it helps with spacing issues (though it also increases their susceptibility to AoE attacks). Raptors also have the pack tactics (and can apply it at times when wolves can’t due to space limitations), and deal slightly more damage than the wolf.
The downsides are one less hp (but shepherd druids turn this the other way from lvl 6, as raptors have 3 hit dice and wolves only 2), their size making them more vulnerable to various pushy-grabby tactics, and the wolf’s ability to knock enemies down for allies to get advantage. The wolf works very well in supporting party melee for this reason, something you won’t get from the raptor. The size also means that medium or larger enemies can wade through raptor spaces, making them less a wall of meat than a mild inconvenience of meat. On the flipside, the raptors can slip through many enemies’ spaces, too.
Wolf: The standard conjured option for the tier, as wolves are usually readily acceptable to the DM, and can do well in climates from desert to tundra. Individually. they are mediocre fighters and somewhat fragile, but they come into their own when fighting alongside other melee. Wolves can help your party melee by knocking enemies prone (make sure your ally has their turn between you and the enemy), and other melee help the wolves by activating your pack tactics.
CR ½ is accessed at level 4 for normal druid wild shape, meaning it may still make good sense to put on an animal form and fight, especially when you’re low on spells. Conjure Animals can get you four of these for a third level slot if you want a bunch of apes to pelt your enemies, or if you need warhorses for your party. Defensively, most beasts here are very similar, with 19hp and 11 or 12 AC. The jaculi has better AC and slightly fewer hp.
Ape: Decent all-rounder, and the only wild shape that has a ranged attack, though the melee attack option is twice as effective. There’s also a climb speed to help you if you come up against enemies with strong melee but weak missile capability.
Black Bear: Slightly faster than the ape, and potentially harder hitting. Without errata, it aims worse than anyone else in the tier.
Crocodile: If you have a speed boost to overcome the sluggish ground movement, you may like the restraining grapple effect of the bite. Crocs have unimpressive basic attack damage to compensate for that advantage.
Giant Goat: When charging it deals as much damage as the ape, and it has the same AC and hp, with faster movement. It is only actually better when you want to knock people prone or avoid the same happening to you (well, no help against shoving, unless your DM decides to be a little generous with the 'surefooted' ability). Or when you encounter someone guarding a bridge: Have the bard tell them
this tale, while you take this form.
Jaculi (ToA): A rare snake that neither kills with venom nor coils around its prey. As a surprise predator, these are good at lying in ambush, though less good at moving into an ambush position, as their advantage on Stealth only works for hiding, not sneaking. They are deceptively mobile in combat, as they can make a Spring attack, allowing them to move 30’ as part of their attack, leaving them their normal movement in addition. When using this Spring, they deal pretty good damage for the tier, but lose some in a slugging match. They have climb speed and 30’ blindsight.
Jaculi have only 16 hp, but at AC 14, they are still less vulnerable than others in this tier. Their precision is a little low, but even their slugging damage is good, only slightly worse than the ape’s.
Warhorse: In a successful charge, the warhorse deals impressive damage, and decent enough for just standing and stomping on people. Very fast, but poor AC. Note the MM errata that fixes its to-hit to +6.
CR 1 is where the moon druids start their wild shape. Land druids can shift to this tier from level 8. Conjure animals can bring two of these along with you for a third level spell slot.
Brown Bear: All-round damage dealer, strong hp, good movement, lousy AC. When in doubt, brown bear.
Crag Cat (SKT p. 240): Very similar to the tiger below (the crag cat has one bettter dex modifier, three fewer hp), but with some anti-magic goodies added on. Nondetection is something otherwise hard to get, and spell turning is funny.
Deinonychus (ToA, VGtM): In a movement fight, where it can get off its pounce, the deino can actually out-damage a brown bear, unless attacking a quite high AC (as its precision is slightly worse). The deino has better AC than the bear, but is also considerably less durable. It has its niche, particularly as wild shape for druids with the Mobile feat (or for coolness, though I personally rate bears every bit as cool).
Dire Wolf: Good hp and AC, a little on the low end damage wise. Has pack tactics, so works best in groups. Pretty fast.
Female Steeder (OotA): Decent defences and a venomous attack. Not the most obvious of combat forms (though not terrible, either), but between being able to jump a staggering 90', spider climb, 120' darkvision and +7 stealth, you may well find uses for this tarantula form. There's a monstrosity version in MToF, so the critter you see may or may not allow you to take this shape. Ask your DM.
Giant Eagle: On the wing, this is the fastest beast form in the MM. It is also the most durable flying beast, able to deal respectable damage for the tier, even compared to ground beasts. Since the giant eagle has a language, you can command conjured minions while in this form.
Giant Hyena: Big hp pool, decent damage, pretty fast and with the interesting Rampage ability, which lets you run a bit and bite again if you down an opponent.
Giant Octopus: Theoretically possible choice, but many tables (including mine) would consider this cheese as well as lacking the right narrative tone. If your table feels otherwise: Huge hp pool, able to hold its breath out of water for a while, 15 foot reach and so able to grapple enemies where they can’t hit back (though
Crawford doesn't like that bit of cheese). 10’ land movement makes it sorely in need of the Mobile feat or a Longstrider spell.
Giant Spider: Fragile hp, but good AC. Has Spider Climb and various web abilities. Also deals decent damage against those who aren’t too resistant to poison. A bit of blindsight and 60’ of darkvision.
Giant Toad: Solid hp, interesting choice for swallowing your opponents as a means of battlefield control. What happens if you revert to caster form after swallowing an orc? I guess there's only one way to find out.
Lion: If they can get all their little ducks in a row, lions are pretty good. They pounce, have pack tactics, good mobility and +6 stealth. But when they fail, they deal unimpressive damage and are fairly vulnerable.
Tiger: A heavier version of the lion, less mobile and vulnerable, slightly more likely to deal good damage solo. Has darkvision for some reason, and the customary +6 Stealth for a big cat.
CR 2 is the form most druids cannot wild shape. The damage output becomes a major consideration for the moon druid here, as the other melee get their second attack around now, and the druid is rather stuck for ways to increase damage beyond picking animals that deal more. Conjure animals can bring one of these beasts to your aid for a third level spell slot.
Allosaurus: If the pounce can be made correctly, this dino deals impressive damage for the tier. But it is a gamble, as it leads with its lesser attack in a pounce. Allosaurus has AC as can be expected (i.e. poor), but a good hp pool. The real advantage to this creature is the movement rate (or the coolness factor - it’s a goddamn carnosaur), but between its mediocre slugging damage and risky charge, I’d probably pass this one by for other options.
Aurochs (VGtM): Nearly identical to the same-tier rhino, a charging form. The aurochs is faster, and in balance has fewer hp.
Giant Boar: The poor cousin of this tier. It’s simply surpassed in every regard, having only the passive/responsive Relentless to fall back on to make it special.
Giant Constrictor Snake: Huge; but maybe the DM will cut you some slack because of its suppleness and shape. Impressive hp pool, mediocre damage, but does hinder the target considerably, with a fairly high DC to get out of its coils.
Giant crayfish (TftYP): Fills out a niche in the tier, with decent defences for a beast, and some considerable control options to boot. Blindsight can come in handy. Has rather poor aim to balance its advantages.
Giant Elk: Huge; four-footed, lumbering brute. If you ever wanted to stomp people to death, here’s your chance, because the giant elk is good at it - at least against prone enemies. It has poor hp but compensates somewhat with the best AC in the tier (don't ask me why). In a slugging match it is highly dependent on the enemy being prone for its damage to be good. Setting someone's speed to 0 means they can't get up from prone, and getting them prone in the first place can be done e.g. by using this form’s charge, allies using Shove, or maybe summoning some (dire) wolves. Having a language in giant elk form, you can command those wolves if you do conjure them.
Plesiosaurus: Another case of an aquatic animal which can function above water and has a bit of land movement. If your DM is like me, s/he won’t like the image. If your table is fine with it, plesiosaurus has huge amounts of hp and decent AC for the tier, and it even deals reasonable damage with reach. Consider buffing its movement, it could use it.
Polar Bear: If you can get the cave bear version, those are strictly better. That said, this bear is the glass cannon of the tier. It deals big, reliable damage, but has poor hp and AC. When in doubt, polar bear.
Quetzalcoatlus (ToA, VGtM): Huge. A bigger flier even than the CR 1 giant eagle. Having flyby attack and a dive-for-extra-damage ability, this Huge flappy bastard does well in hit-and-run against land-based melee, and it won’t get as much in the way of your allies as many other Huge forms or summons. Be advised: In a slugging match, it does not outperform the CR 1 giant eagle, with one less to-hit and less damage overall, and only four extra hp in its pool.
Rhinoceros: The reliable charger of the tier. Not great on hp or AC, but can lay down good smack when charging. In a slugging match, it does just a tad better than the allosaurus because it hits better, but it does not hold a candle to elks or bears.
Sabre-toothed Tiger: Very much like the allosaurus; slightly less risky in the charge (leading with its good attack unlike the allosaurus), but also slightly less powerful in slugging matches. +6 Stealth for being a large cat.
CR 3 has only three MM beasts, one of which is a whale. Moon druids can take these forms from level 9, but they get elemental shapes at level 10, leaving a rather small window - although elemental shapes do use up both your wildshape ‘charges’, so there’s that. CR 3 is too much for Conjure Animal, but Conjure Fey could let you summon from this list. It could do much better for you, though (CR up to the spell slot used to cast it, and not just beasts). Still, for what it’s worth:
Ankylosaurus: Huge. This dino has solid defences for a beast, and an attack that knocks opponents prone, something that may make your melee allies happy but makes the archers annoyed. Does not deal more damage than CR 2 bears and elks, but has better AC and far more hp.
Giant scorpion: A bit of a gamble. Hp pool comparable to CR 2, aims like CR 1. But it has AC 15, and can deal good damage if it does manage to hit enemies not too resistant to poison. In most situations, it won’t compare well to CR 2 bears or elks. But the grappling claws may be useful under the right circumstances.
Giant Snapping Turtle (ToA): The nearest MM equivalent is the ankylosaurus above. The dino has fewer hp and worse AC (at least compared to right-side-up turtles), but has slightly better to-hit, and the ability to knock enemies prone with its attack. So the turtle is somewhat tankier, and loses mostly the control element for it. The turtle also has a nice 40’ swim speed and can breathe both in air and water.
CR 4 in the MM consists of the elephant, which you can summon with Conjure Fey (though I don't see why you would, stats-wise).
Elephant: Huge. In a slugging match, they do slightly worse than CR 2 bears, despite having better to-hit - they do a little better against prone targets. But they also have the option of charging, which leads with tusks and forces a pitiable DC 12 strength save on the victim to avoid activating a stomp (which is where the better part of elephant damage lies). For wild shape you may also take into consideration the elephant’s agile trunk, which can be very useful out of combat.
The elephant has slightly more hp than the CR 3 options, slightly less than CR 5, as could be expected. It has worse AC than those two tiers.
Giant coral snake (GoS): Size large, but it is still tankier than the other options in this tier due to a larger hp pool and comparably good AC. It deals little damage with a poor to hit. There is a juicy stun rider on the bite, but between the poor to hit and the weakish save (Con DC 12), this is unlikely to be generally dependable. There is also a 30' swim speed and a bit of blindsight. The madness is utterly DM dependent, and unlikely to do much in a straight fight.
Giant subterranean lizard (TftYP): Huge. I love this one. This is only the third CR 4 beast I’ve seen, and so it is much appreciated. Though it has fewer hp than the VGtM stegosaurus and the MM elephant, it has three different means of control to the elephant’s one, and the lizard can use them all without charging. Its damage is fully comparable to the stego’s in a slugging match, and surpasses it if any of its control effects are taken into account. It even inches out both stego and elephant for AC.
Stegosaurus (ToA, VGtM): Huge. Outperforms the CR 4 elephant in slugging matches both in damage and slightly in tankiness. It loses the charge-for-knockdown-and-stomp-in-the-face in balance.
CR 5 is a small club with three MM members. One is aquatic and shan’t be mentioned here. You could summon one of these with Conjure Fey if you don't fancy a mammoth.
These shapes are the first beasts that can really compete with elemental forms in terms of damage.
Brontosaurus (ToA, VGtM): Gargantuan. This contested sauropod is considerably tankier than the Giant Croc below, paying it off with less control and damage. The brontosaurus has an impressive 20’ reach, which could be useful (attacking past an ally, or attacking enemies in melee who can’t opportunity attack when you move away after) or annoying (letting enemies roam a vast area without provoking opportunity attacks), depending on the circumstances.
Giant crocodile: Huge. You can’t tail slap people you have in your mouth, but releasing a grapple doesn’t cost an action, so you should be able to lay down the smack on a single target if you so choose. Tail slap first (ideally knocking the target down while you're at it), then put your enemy in your mouth with a bite, and keep it there for its turn. If you grapple a prone opponent, they can't get up again until they break the grapple. Unimpressive hp, and AC above average for beasts (but still quite poor).
Hulking Crab (SKT p. 240): Huge. The only beast I've seen that has a native AC (17) better than Barkskin (16). Shell camouflage is interesting in that it takes Int, not Perception, to see through this 'stealth', which can be used in the open - open water at least, depending in the DM.
The giant croc has harder control, more hp, and better damage due to hitting better, so it won't be for those reasons you want this crab.
Triceratops: Huge. More hp than the croc, one worse AC. Hits slightly better, but deals much less damage in a slugging match. Its charge leads with the good attack, but the DC to avoid being knocked prone (and potentially get stomped on for about 22 damage) is an unimpressive 13.
CR 6 is a single-elephantidae tier. Conjure Fey can give you a a mammoth, but don't lose concentration or you'll wind up in traction. Summoning an elemental with Conjure Elemental is probably a better use of your resources.
Mammoth: Huge. The mammoth has hp like an earth elemental, though not the AC or the weapon resistances. It has an impressive +10 to-hit (two points better than the best air and earth elementals; though not so impressive compared to any dedicated melee comrades you have). Without that, the mammoth deals slightly less damage in a slugging match than the elementals (and still less than the giant crocodile and the brontosaurus) unless fighting a prone enemy. The mammoth is a charger, however, and the DC to avoid being knocked prone (and probably trampled for another 26 damage) is a healthy 18.
Fortunately for moon druids, by now they have Beast Spells, and can cast many spells in wild shape, so some of the earlier forms come into prominence when damage dealing becomes less crucial.