It depends on how long you expect it to live. Will you buff it or not? Does your opponent play a bunch of fragile creatures or just a few very tough ones, or none at all?
You could get around the Monster killing allies with immaterial creatures: Immortal, Phase Dragon, Ball Lightning, Fractal, Monster would work.
Other methods:
Photon, Immolate, Phoenix, Seraph, Rain of Fire, Monster
Graveyard, Bonewall, etc. Monster (Doesn't matter if he destroys these.)
Anything with Chaos Power, and Mutation for when he gets out of hand.
Lots of other stuff would work too.