Exactly when can you use an immediate action

[Christian]

Just adding fuel to the fire: if the character teleports after the attack roll but before the damage roll, is the monster's attack gone? Or can it now use it against another opponent within reach? And if the latter, does it have to use the same roll?

 

[Hypersmurf]

In fact they (AoO) "interrupt" the opponent's action before "completion".

Ordinarily, but Karmic Strike appears to be an exception - it doesn't interrupt, but rather occurs simultaneously.

-Hyp.