I'd like to touch on something that was brought up earlier on in the discussion. The idea that the more a monster gets hit may build a third meter probably a rage meter.
My idea is that as you get hit, the meter will spike at each hit instead of continuing to build incrementally akin to a Street Fighter super bar.
Each hit will make the meter spike more, so the attacking monster wants to deal damage but be wary of the rage meter. The defending monster wants to reduce the damage taken, but if they are in a tough spot they can take advantage of where their rage meter is at before it goes back down. Try to visualize each spike in the meter like trying to fill a meter by tapping a button as fast as possible, each second that you are not pressing the button it is already decreasing at a rapid rate right?
What will the defending monster be able to do as the meter fills? I propose that there are three sections of the meter and that the more the meter is filled the more options are available. Think Unholy War by Crystal Dynamics for PS1.
http://www.youtube.com/watch?v=R8tS6VPYCYc start viewing at 2:26
First section- A stronger or EX version of a normal attack
Second section- A unique advantage or buff. Defense/Health/Attack/Speed boost that would expire over time.
Third section- Rage attack such as Final Breath.
To avoid abuse/overuse of rage you may either need to trigger "rage gathering mode" somehow, and it would probably have to have a cooldown of sorts.
Any ideas to expand on this?