Savage Attacker

[ATHATH]

That is pretty decent. That's about +11 damage per turn. What form do they have that deals 4d10 on a single attack?

Dunno about 4d10, but a lot of the CR 2 Beasts get one attack per turn that does massive damage. The quetzalcoatlus, for example, can do 6d6+2 damage with a single attack if gets the damage boost from Dive Attack.