The +2 circumstance bonus is fine. Might as well make them tougher!
And on that note, your second ability line is good, too.
Updating the Gladiator Lizard.
What other special abilities do you want to add to these?
Well I was slightly tempted to have it get iterative attacks with its talons as though they were weapons, plus bonus feats for perfect two-weapon fighting, so its Full Attack is a pair of +12/+7 talon attacks or a +12/+7 talon plus a +12 talon instead of it just being two +12 melee attacks. Probably while forgetting that pesky off-hand weapons use half damage bonus rule.
That's probably going too far though.