This would be good if
1) Ravids did this. They don't due to low intelligence and inability to planeshift. That is not to say that nothing does through.
Only creature from the positive energy plane I know of. :-/
A robot would be more intuitive.
And it would be gravity. I might change this, but only if I cannot find a way to fit this in Light properly. The point here (in this serie) is to enhance certain synergies between elements, enabling some other options and powering up stalls. Making it a gravity cards would make it terribly overlap with flying Titans. They both can grow, but Titans would probably be the best choice here by far, with their huge hp covering up from the lack of immaterial, and acceleration more than making up for the lack of a growth mechanism. They would work almost the same, but the Titans would probably be better due to momentum, possibility to play catapult, higher attack and faster/more constant damage.
@Patch: That's... lovely.