Conjure Animals Encounter CR

[ZenBear]

I'm working on some homebrew spellcasters, and I want them to have Conjure Animals on their spell list. The question I have is, how do I balance an encounter with this in mind? The spellcaster is only CR 2 by itself, but it can conjure 8 CR 1/4 beasts which immediately turns a Medium encounter for 4 2nd level characters into a Deadly encounter for 4 4th level characters. I understand the party would sensibly focus the caster, but if the caster maintains distance and concentration then it's an easy TPK. How should I handle this? Is it a bad idea to put this spell on a monster? It really fits the spellcaster in question, so I really want to grant it.

[Rukelnikov]

The spellcaster doesn't necessarily have to summon 8 of something, it's could be 4, 2 or 1, making the encounter less deadly. Also if it's gonna open with that maybe just tally the xp as if every monster was part of it, but halve it on account of the "weak point"

[Xihirli]

NPC spellcasters can break a few rules. In this case you could make a weaker version of the spell, and halve or reduce the number of beasts.

[Tanarii]

My experience is player definitely focus fire any caster that conjures animals. With everything they've got.

[Great Dragon]

Greetings!

The first thing to keep in mind is that Monsters and NPCs don't follow the same rules as Player Characters.

Now, your putting the Spellcaster as a CR 2.
It also depends on how many times they can cast Conjure Animals.

Ok, the Evil Mage (Lost Mines of Phandelver in the Starter Set) is CR 1, and is a 4th level caster.

So, making your Caster a 5th level Druid is most likely a CR 2.

Suggestion

Hit Points: 35

Save: +5 Wis.

Str 12 Dex 12 Con 14 Int 10 Wis 17 Cha 10

AC 15 (Hide, shield, Dex) or
AC 16 Barkskin (Wild Shape)

So, able to cast (if chosen like a PC)
3 Cantrips: Produce Flame, Shillelagh, Guidance

4 First level. Cure Wounds, Entangle, Faerie Fire.

3 Second level. Barkskin, Hold Person, Moonbeam

2 Third level. Conjure Animals. Call Lightning.

****

Now, you are correct, in that a swarm of 8 CR 1/4 beasts (wolves) can overwhelm a 4 person party.

But, with the low AC 13 and 11 HP taking one wolf down isn't too hard.

This can encourage players to work together to either take down the wolves or focus on the caster in order to break the Caster's Concentration.
This also applies to Call Lightning.

[ZenBear]

For context, this is the stat block of the caster in question. It's a Plague Priest, from Warhammer: Fantasy, that I'm converting to 5e. I want it to have a version of the Vermintide spell from Total War: Warhammer where they summon a unit of clanrats, but in this case I'm thinking Giant Rats (Diseased) or Swarms of Rats. I intend to use these in multiple campaigns, so party composition will vary.

Armor Class 12
Hit Points 91 (14d6 + 42)
Speed 35 ft.
STR 10 (+0) DEX 15 (+2) CON 16 (+3) INT 10 (+0) WIS 16 (+3) CHA 8 (-1)
Damage Immunities Poison
Condition Immunities Poisoned
Senses Darkvision 60 ft., Passive Perception 13
Languages Common, Undercommon
Challenge 2 (450 XP)

Sunlight Sensitivity. While in sunlight, the skaven has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.
Keen Smell: The skaven has advantage on Wisdom (Perception) checks that rely on smell.
Pack Tactics: The skaven has advantage on an attack roll against a creature if at least one of its allies is within 5 feet of the creature and the ally isn’t incapacitated.
Tough: If damage reduces the plague priest to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is from a critical hit. On a success, the plague priest drops to 1 hit point instead.
Pestilent: Devotees of Clan Pestilens are immune to the effects of poison and disease, though they remain capable of carrying such afflictions.
Spellcasting: The Plague Priest is a 5th level caster. It’s spellcasting ability is Wisdom (spell save DC 13, +5 to hit with spell attacks). It knows the following spells:

Cantrips (at-will): Infestation, Poison Spray, Spare the Dying
1st level (4 slots): Bane, Ray of Sickness
2nd level (3 slots): Blindness/Deafness, Ray of Enfeeblement
3rd level (2 slots): Stinking Cloud, Vermintide (Conjure Animals - Rats)

Actions
Multiattack: The plague priest makes two attacks with its plague censer.
Plague Censer. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 3) piercing damage, and the target must make a DC 13 CON saving throw or contract a disease. Until the disease is cured, the target can't regain hit points except by magical means, and the target's hit point maximum decreases by 3 (1d6) every 24 hours. If the target's hit point maximum drops to 0 as a result of this disease, the target dies.
Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 4 (1d4 + 2) piercing damage.

[Great Dragon]

I'm not familiar with Warhammer, so can only give D&D examples.

I'm thinking that the 91 HP (14d6 +40) is closer to a CR 8.

For a 5e D&D CR 2, between 5d8 or 8d6 (plus Con) might be better.

****

The diseased giant rat can work for straight Conjure Animals. Netting eight per casting.
So, depends on how many times the summon spell can be cast.

Swarms are a little trickier.
A Rat Swarm has at least 20 "normal sized" rats (figuring 1 HP each) in it, and covers an area which affects multiple creatures.

Individual rats cannot usually be targeted, instead all attacks affect the entire Swarm.
The DM decides if damage reduces the number of rats in the Swarm(1), or if only reducing the Swarm to Zero HP eliminates it.(2)

The first option means the DM does more paperwork tracking number of rats in relation to the new size of the Swarm, and then deciding if that changes the Swarm's damage.

The second option is tougher on the PCs, since the Swarm is just as effective from the start of the fight to the end.

[Dalebert]

Folks are always quick to point out that you don't get to choose what you summon. The DM decides. Why would that be any different for an NPC? Just pick fewer creatures of a higher CR.

I had a DM who ruled no more than 4 creatures ever, but he let me pick what I wanted. He never changed the creatures. So I typically picked 4 CR 1/2s or 2 CR 1s, like dire wolves.

[Great Dragon]

Folks are always quick to point out that you don't get to choose what you summon. The DM decides. Why would that be any different for an NPC? Just pick fewer creatures of a higher CR.

Upon research, I only found
PHB 225: "The DM has the creatures' statitics".

Nothing saying that the Player could not pick what was Summoned, only the CR limit.

This is also true for:
Conjure Celestial
Conjure Elemental
Conjure Fey
Conjure Woodland Beings

As always, the DM has final say for their game.

[Dalebert]

This is what it says you can pick, cut & pasted:

Choose one of the following options for what appears:
* One beast of challenge rating 2 or lower.
* Two beasts of challenge rating 1 or lower,
* Four beasts of challenge rating 1/2 or lower.
* Eight beasts of challenge rating 1/4 or lower

It never says you get to pick specific beasts; just their CR ("or lower", i.e. DM can lower it) and #. So I have to correct myself a little. You get to pick the #. DM might lower the CR. So he could say don't pick 8 creatures our you'll get CR 0 rats or something.