Is it legal? is it allowed?

[RigaMortus2]

I thought I read somewhere (perhaps the DMG) that stated you can only use attack powers on something that is a "credible threat", to avoid situations like the old "bag of rats"...

Found it, here we go

DMG p. 40, the "sack of rats" rule:

When a power has an effect that occurs upon hitting a target - or reducing a target to 0 hit points - the power functions only when the target in question is a meaningful threat.

Is your ally being a meaningful threat towards you?

 

[Rechan]

I'd allow it. The paladin is wasting a daily, targeted ally is taking damage and the paladin has to use up his minor action to sustain it.

Is your ally being a meaningful threat towards you?

So I guess that the wizard can now throw area attacks into melee without worry about hitting his allies! SCORE.

 

[HeirToPendragon]

So I guess that the wizard can now throw area attacks into melee without worry about hitting his allies!

No. But that's a nice way to twist words to support your interpretation.

 

[dammitbiscuit]

If you can hit your ally by accident, then you can hit your ally on purpose. It's up to the individual DM to determine if being a "willing target" changes the attack or not, and if so, how, because there aren't rules for it currently.

 

[IceFractal]

Target: one creature specifically means it can be used on yourself, an ally, or an enemy. If it was "one enemy", as some powers are, it would mean an enemy only, and if it was "one ally", you couldn't target yourself, but it is none of those.