Biggest problem with Chimera (Kai-mer-a as opposed to Cheem-er-a) is that its a Bomb. You don't use it until the last minute to protect it, and then it wins you the game if you have more Atk then the opponents HP, shield or otherwise. Your opponent wont get a chance to reverse it.
The other option is to dive then play Chimera, but crossing elements to bomb when you will win without it seems pointless.