The "Pain" spell is: Target enemy model within 12'' takes 2 hits with AP(4). Most of spells/abilities refers to units. In this case, can I select hero attached to a unit as a target? Seems to be very powerful.
but the effect of the spell is already clear, in plain text. you pick a model to hit with the spell. it doesnt need sniper. and it doesnt have a hit roll, so part of the sniper rules is irrelevant and is going to raise questions from why a SPELL has something mentioning a hit roll. There is no issue here.