I said darkness, fire and gravity, in that order. Antimatter thoroughly destroys vampires, while mutants ruin devourer spam (and pandemonium too, unless they have earth mark for burrowing). Maxwell's daemons kill all fire creatures, antimatter really hurts them (because of their high attack). Gravity's momentum gets stopped by antimatter, their large units and oty's get mutated, and their shield only blocks upgraded dragons and werewolves/lycanthropes (and probably many mutants). Butterfly effect is good against all three, but not as good as it is against life, time and rainbows (though life favours more units, time can rewind you mutants and rainbows can counter practically everything given time, so they don't make it into the top 3).
Actually entropy isn't that good against gravity now that I think about it, it's just much better than most other elements in that match-up.