what about putting a certain HP requirement for it to trigger??
something like "When user's HP reaches X, creature with highest HP gains gravity pull"
i'm not sure if this is a buff or a nerf, but i think it is both..
there are times where you wouldn't want your creatures to die (yes, i'm talking to you, modified RoL/Hope and you too, VaderSader)
just my two cents, ignore if you please XD