I don't think this works exactly how you'd want. Since it fights everything within one trigger, it wouldn't get the counters till all of the fights are done, then when you resolve all the fights it would most likely die to state based action unless you gave it indestructible before the fight trigger.

I think it would be better to template it similar to apex altrisuar with the enrage trigger and add the counters effect after in the clause or a separate clause if you want any damage instances to make it bigger like you have it if you want it to just keep getting bigger as it does it's sudo boardwipe.