Weird counters to weird builds.

[Axoren]

I was thinking about it and I thought it would be a fun-little activity:

Find some random item, spell, or effect which, while mundane on its own, will be a hard counter to a very niche build.

For example, Bestow Weapon Proficiency against an Improvised Weapon build, like the Fighter (Cad) or Disarm + Catch Off-guard.

What others can you think of?

[Boomerang Nebula]

Do you mean inventing new rules? For example wearing garlic makes you immune to vampiric touch.