I agree with Drake. This card should be bigger (hp wise) both thematically and functionally so people have to work to take it down. At least for the upped version anyway. I like giving gravity a means to hide creatures from sight.
An interesting twist would be to have it grant invisibility at the beginning of each turn. That way, the enemy can use invisibility dispelling spells to see things, but only for 1 round. E.g. this casts a massive shadow, so nearby enemies can only be seen in the wake of the splash of light / magic created by mass effect spells like pandemonium or firestorm.
Either way though, this looks like a really cool card and would make a very valuable addition for gravity.