All Dynamis mobs are unusually large. At least, all the one's I've seen pictures of. I've yet to see snapshots of the mobs from beaucedine/xarcabard, but I'm guessing they're also huge. Dynamis is supposed to be scary. And it is. :)
All the NM in dynamis are bigger than the nm not in dynamis. All the normal yagudo mobs in dynamis are regular size. And memphis is the person who runs all dynamis for NA on siren.