pyro
if there is a sneaky pyro he can tear your team to shreds (backburner exist for a reason)
if there is a flare pyro he will ruin your sniper's aim
if there is a skilled pyro he can reflect your projectiles back to you, making your crits BS
if there is a pyro who knows his shit he will kill the medic before anyone else
also making uber useless unless using the overhealer (but who uses that useless garbage)
also makes spy useless AF (not like spy had a use in the first place that useless french bread)