Grommloc supersized and fearing any who stand in his way
He doesn't have any idle animations, but he will do a small roar and fear wild pets and critters around him. The large groups of critters in Valley of the Four Winds is a good spot to watch him do his thing. Weaklings, flee puny critters! :P
I did try to get him to scare away some level 1 cows in Stormwind, but they didn't seem phased by Grommloc's savageness. Cows are fearless...? lol
I've yet to level and try out Grommloc in battles. I don't PVP so his breed (P/S) probably won't matter too much for me. Not even sure P/S is good for his set of abilities. But I suppose that's ok if it's not. Pets that cost RL money that are amazing in battles due to a strong breed + strong moveset can be controversial.
All pets in general are "must haves" for a collector, but a "pay-to-win" pet that changes the metagame upsets the balance and perceived fairness since some will be able to afford it while others won't.
So if Grommloc doesn't have a very good moveset and/or breed, I'm ok with that. It's fine if it's just a fun vanity pet that will hang out with you and scare away cowardly critters. :)
And on an unrelated note, developer Jeremy Feasel dropped a hint of what's to come at BlizzCon. I'm excited and can't wait to learn more!