I wouldn't mind it actually, but even better, how about raid bosses as legendary's. Catching the Pheonix as a monster to use in battle. Maybe adding some sort of limiter for certain captured monsters. Like one monster will be your main choice for constant actions, one for heavy attacks most likely on cool down, and one like the Pheonix that's your extremely heavy attack that's on a really long cooldown or special proc (maybe a limit break).
