[Xargon]

It increases duration and power (where applicable) of every non-combat spell (i.e. spells that are not direct damage spells), afaik. Additionally, it increases the power of quite a few unit abilities or stats (all summoning stuff, I think). So yes, it is crazy powerful and gives a huge boost to the short-lived (de)buffs.

edit: I just realized that it extends Phantom for two more turns as well... because that spell clearly wasn't powerful enough before. (I got it on Merlassar, so did not notice this before)