Shenanigans! SHENANIGANS!
(I tried to submit that as the entire review, but was informed it must be at least 200 characters long. So now I'm adding more characters about pretty much the sole reason for this card's existence is enabling shenanigans. I mean, sure, you could Desperate Alliance away Lore Aragorn to reduce someone else's threat, but where's the fun in that? Play a dual-sphere deck and Desperate Alliance away a hero from your "minor" sphere to enable playing cards that require all heroes to belong to the same sphere. Play a 2-hobbit deck and Desperate Alliance away your non-hobbit hero so you can play Hobbit Sense. When you're down to your last hero, engage everything and Desperate Alliance him away, then take every attack undefended. With no heroes under your control, the damage has nowhere to go, so it all just fizzles. Are these combos worth the amount of setup involved? Probably not, but come on... the shenanigans!)