Is the gravity pull on this creature an effect or ability (active skill)? In other words, does it start with gravity pull being applied on it, or does it have that as an ability? I'm hoping it is the former, since it should at least be gravity pulled to allow it to be killed.
Nevertheless, we can change what creature has gravity pull by simply using gravity pull on another creature.
I can think of a rather powerful situation where we can play like some weak creature with over 0 hp and a bunch of BoLs and some cheap, high damage creatures like giant frogs and then consolidate them all into one chimera and play quintessence on it. One could easily have an immortal chimera dealing 30+ unstoppable damage that cannot be killed because we can simply play gravity pull on a ball of lightning to take the gravity pull off the chimera.
It's this quint + switching gravity pull combo that scares me a bit and possibly seems a bit OP. Normally it takes a great deal of time to be able to deal 30+ unstoppable damage from a truly immortal, completely unkillable creature (ex: immortal unstoppable lava golem would take 12 turns of growth to deal that much damage), but with chimera it should be doable in much less time.
In fact, that's the first kind of deck I want to create using chimera: a trio deck (fire + gravity + aether for quint) but only with gravity pillars (fire from cremations and high damage creatures and we only need one quintessence for the chimera). Maybe SoGs + a little CC/shield to stall things a bit for the super unstoppable, undestroyable chimera to come out. Either that or maybe a speedbow using low-cost, high damage creatures and some stalling to buy us time for the chimera + gravity pull + quint combo - speedbow seems a bit faster actually.