We have a real problem with a DM who has a hardon in us fighting Deathknights and Antipaladins what kind of character could i build counter his foolishness.
I would be able to build up level 11
1} This is in General Discussion, so it'll get moved. Hopefully you can find it after.
2} It may get moderated due to one particular word-choice. Doesn't bother me, but others may object.
3} What's foolish about throwing deathknights and/or antipaladins out as opponents?
4} Pathfinder 1? Pathfinder 2?
5} What do you mean by "counter"?
Deathknights and Antipaladins are fantastic antagonists!
Though I think it is generally more fun and interesting to build a character that fits a concept you enjoy than specifically building it to counter a specific threat - having a character face a threat that is asymmetrical to them and figuring out how to defeat that opponent with the abilities they have is a lot more fun and challenging that tailoring your character to that opponent.
If you absolutely must tailor a character to a specific opponent, I would suggest a Champion, Rogue or Ranger, as they are classes in which dedication to slaying a specific opponent can be an actual part of their theme in a way that makes sense.
(I am going to assume PF2 here as it is the current edition).
For a champion, either the vengeful oath or shining oath feats help you to represent a paladin who opposes the undead or antipaladins specifically, and many of the spells and abilities of the class specifically target evil or undead opponents.
For the Ranger, PF2 doesn't have the option to use the favoured enemy feat on undead, but simply being a ranged combatant who is good at focusing on taking down a single enemy helps them a lot. A PF1 ranger can obviously take undead as their favoured enemy, or take archtypes that specialize against undead.
For the Rogue, the ability to try and take out a single powerful target is fairly self-evident in what their class does in either edition.
An honourable mention goes to the pf1 inquisitor to being a specialized hunter of the wicked and undead.