Kaodi
Legend
A level 20 fighter could have, what, an AC of 41 with +3 full plate, an indestructible shield (13 hardness), and possibly infinite block reactions? So to get a failure instead of a critical failure you would have to hit 32, so you would need a natural 20 plus an attack bonus of +12. I think there are at least a few level 3 creatures that could hit and damage that. So if you had 10,000 of an appropriate level 3 opponent versus a defence optimized fighter I think the 10,000 could win,
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Edit: Ack, I forgot the fighters proficiency bonus ncreasing. So, uh, no, the 10,000 would be completely boned.

Edit: Ack, I forgot the fighters proficiency bonus ncreasing. So, uh, no, the 10,000 would be completely boned.