This has come up numerous times in my games...
If a monster has "[surge] Blast (if at least 1 additional hero is affected)" and it meets the criterion, i.e. more than one Hero is affected, is it legit for the Monster to use it even if doing so would damage/kill other Monsters including itself?
I've been playing it as RAW... i.e., the criterion of multiple heroes is met, therefore the Monster activates blast, but this is usually more beneficial for the Heroes rather than the Monsters...