The Power of a Power
Our GM limited our characters (during this building time) to one power. Spells are a little different, but that is not something I need to worry about.
The power that fit my character was:
Invisibility (Sight Sense Group, No Fringe)
Limitations: Chameleon
If I recall the power eats 6 to 7 END per Phase with my character total END of 30.
I could get away with using it in the begining of a battle, but droping it soon after or taking a recovery durring one of my Phases to keep it active.