Let's do a battle, where we pit characters with the most vaguely defined powersets. There's two battles to consider here. Who wins the CONTEST of "MOST VAGUE / INDETERMINATE" powers, and secondly, who wins in an all-out fight to the death? Feel free to add your own contenders to this roster that I have lined up.
It's nearly impossible for me to ever tell exactly where High-Evolutionary fits in the grand 'tier' of things. He's so ill-defined. But I think Mikhail Rasputin takes the cake for most vaguely defined powers. Even in AoA, as a Horsemen, you had no idea what he really "did". That said, I think out of these 3 guys, Apocalypse wins in a fight.