A KO'ed Bastiodon

[pokeprofRaymond]

I have a question on Bastiodon and its Anger Revenge attack.

If Bastiodon was KO'ed by an opponent's attacks, does it still do 40 damage to one of your opponent's benched Pokemon?

 

[PokePop]

I don't think you're understanding the timing.
The bonus 40 damage is part of an attack. It is done at the time the attack is done.
If Bastiodon is KO'd, it is no longer around to do an attack on your turn.
Also, if you have another Bastiodon available, it doesn't get the benefit. It is a self-reference, it does not mean "any" Bastiodon.