glass said:It can kill them!
Depends on how much damage you do, their hit points, etc...
Seriously, the rules assume you are constantly looking for opportunities to attack (and defend from) your enemies but not your allies. Without that assumption the whole combat system breaks (in any edition) -one little power is the least of your worries.
glass.
Disagree. I've never seen a rule where AC, etc, changes because you say "I'm going to attack the fighter, not the orc." Maybe this is part of a complex plot. Maybe you're just pissed at the fighter. Maybe you're mind controlled. Maybe you need to burn the green slime off the fighter's arm with a torch, and he's fighting an orc, and the DM rules you need to make a 'to hit' roll in order to do so, since the fighter can't stop and just let you burn him in combat.
Having powers which magically do/do not affect certain targets based on whether, from round-to-round, they are 'allies' or 'enemies' is a serious immersion breaker, unless the powers have some sort of mystical 'intelligence' (which some might -- though I've always interpreted things like 'heals all allies inside a 30' burst' to be the result of the character consciously choosing whom to heal, and he could heal an 'enemy' if he wanted to...)
You can use 'beneficial' powers on foes. You can use harmful powers on allies. The scope of powers in 4e, and the new tactical depth to the game (this is a *good* *thing*, mind you!) means the opportunity to use a power in a "non standard" way will come up more often, and DMs, players, and game designers all need to be prepared for it.
I might well do freelancing for 4e someday -- so I need to start thinking, now, about "What happens if this cool power I though of is used by one ally on another? If this ability is triggered by X, can a PC cause it to trigger on another PC, and, if so, does that break or unbalance it?"