Let's break Xanathar's!

[Mikal]

Thanks for putting this link. Never understood how coffeelocks really worked before, because I knew there was a cap for sorc points - but there isn't one for _slots_. All I can say is _dang_.

Yup. It's quite an oversight and has been for awhile (see original Coffeelock). The Insomnilock is just the better(?) version of it.

[Silkensword]

Just a fun thing I noticed, in Xanathar's Hexblade it says you get to add your proficiency bonus to "damage rolls" against the cursed target, not "weapon damage" rolls. Stack as many things as you can into one of those attacks! Swashbuckle it up, get that green flame blade, and make sure to hex before, and you will get to add your proficiency bonus a silly amount of times.

[Easy_Lee]

Just a fun thing I noticed, in Xanathar's Hexblade it says you get to add your proficiency bonus to "damage rolls" against the cursed target, not "weapon damage" rolls. Stack as many things as you can into one of those attacks! Swashbuckle it up, get that green flame blade, and make sure to hex before, and you will get to add your proficiency bonus a silly amount of times.

If allowed, combine with the aforementioned coffeelock trick and cast unlimited magic missiles. That's some absurd and unavoidable damage.

[Silkensword]

Gloom Stalker Bugbear with a Greatsword. 100+ max damage on a critical hit at level 3.

[Howl]

Gloom Stalker Bugbear with a Greatsword. 100+ max damage on a critical hit at level 3.

I like this one because it isn't broken at all times, but when it crits on that first turn it crits HARD.

EDIT: I've been thinking about it, and unfortunately I think the build is a bit too MAD, you'd need high dex for stealth unless you're in darkness (Umbral Sight), strength for greatsword damage, then con for health and wis for spellcasting. Unless I'm missing something. Maybe a 1 level rogue dip for expertise and added sneak attack die. Still, you'd be losing out on damage per hit if you dump strength.

[Howl]

I think I've just settled on a build that fits into this theme. Sword Bard 19 / Hexblade 1. With just a one level dip in hexblade you gain shield proficiency for use with the dueling fighting style, the ability to use charisma as your weapon mod, a 1 level short rest spell slot, hexblade's curse and oh, did I mention the Shield spell? So, a bard with just 14 dex in half plate with a shield is able to achieve a whopping 30 AC with a max roll on a d6 bardic inspiration die with defensive flourish at level 4. If you don't want to get disadvantage on stealth you can use a breastplate which still reaches 29 AC max.

EDIT: I made a reddit post about this, here are my thoughts on the build

"...Assuming you hit a 6 on your bardic inspiration roll that is, however even with a min roll you get 25 AC which is comparable to an EK or Bladesinger. This goes up as you gain bard levels, too. Overall I'd say the build is more survivable than an EK even with a lower hit die since they have more spell slots to use with shield, and they're a full caster versus 1/3. Bladesinger is also a full caster, but they are infinitely more squishy at 1d6 HD. Oh, and you get extra attack."

[TheUser]

Thought of a new one!
Courtesy of Jeremy Crawford's unique interpretation of Magic Missile and 10 levels of Invoker you can take 1 level of hexblade to get Hexblade's Curse to add proficiency bonus to that singular roll.

At level 11 (when the build completes) you can use a 5th level magic missile to do 70-91 damage that cannot be prevented without using shield or counterspell.

No legendary resistance, no AC or attack rolls.

Boss killer anyone?

[Bardock here]

Thought of a new one!
At level 11 (when the build completes) you can use a 5th level magic missile to do 70-91 damage that cannot be prevented without using shield or counterspell.

Coffelock cast 5th spells several times
Magic Missales 120 feet (out counterspell range)
Quicken Metamagic + Empowered Metamagic + Magic Missale and Empower metamagic + Repelling Agonizing Eldrich Blast. Boss? Where?

[Renduaz]

>Breaking Xanathar's

>No attention whatsoever paid to spells, mostly to builds

Oh, sweet summer children. The weakest broken spell combination can send all of these builds combined through all the Nine layers of Baator sprawling on their ass in a display of divine munchkinry. I'll make a thread about Xanathar once I've finished reading over it, and boy, Mystra herself is going to be sobbing in the shower by the end of it.

[lperkins2]

Coffelock cast 5th spells several times
Magic Missales 120 feet (out counterspell range)
Quicken Metamagic + Empowered Metamagic + Magic Missale and Empower metamagic + Repelling Agonizing Eldrich Blast. Boss? Where?

Or grab a level of fighter to action surge a second super missile.

[Silkensword]

Oh boy did I just find a gem you all!!!

Have a look at the wording of the Dread Ambusher:
"If you take the attack action on your first turn in combat, you may make another weapon attack as a part of that action"

Well, this is beautiful, isn't it? Three levels in gloomstalker, three in arcane archer, 4 attacks at level 6 in the first round of combat with two bonus actions to buff your attacks!
Of course you can put the other 14 levels in arcane archer as well, giving you two more extra attacks per attack action; the ultimate assassin, and with piercing shot some decent AoE.

Or put 11 into arcane archer and 3 into gloomstalker, leaving you with 6 levels you can play around with some!