The 12 Days of Critmas: The Druid
I was wrong again…
For pretty much all druids, the method of dealing maximum damage in a single turn is the same, so we’ll worry about subclass second this time. Level 8 druids can cast polymorph, becoming a T-rex which can deal 55 damage (4d12 +7) to a single target. As this is a concentration spell, they can drop it for free, and still have a bonus action with which to quicken their highest damage spell. At first, I thought this would be blight, for the 8d8 it deals. However, druids also get access to giant insect, which can produce 10 giant centipedes who all act on your turn, and can each deal a maximum of 24 damage (1d4 +2 +3d6), totalling to 240 points. It's obviously insane to imagine these all hitting, but the spell is still amazning, and this build would probably be usable for a real character. So any druid, regardless of subclass, is dealing base damage of 295 damage. I can’t find a subclass which does more damage with their action; the spores druid can improve it by 1d6 if symbiotic entity is running when they cast polymorph, up to 61. And this beats the other option I considered, taking the Shadow Touched feat for access to inflict wounds, and upcasting this for 60 damage. Feats sadly don’t apply while polymorphed, and the giant insects’ damage is independent of your stat block, so there’s no way to further increase total damage with those free feat slots. For maximum damage on a crit, inflict wounds will outpace the T-rex’s attack, so our final build is a spores druid with Shadow Touched and Metamagic Adept, who can deal a total of 400 damage with crits (12d10 +20d4 +20 +30d6). They're a firbolg. I’m not making any more predictions.