Grendel, from beowulf

[Macrovore]

Attack: +27 Claw (+13 bab, +14 strength)(20 is targeted attack bonus) 1d8+21(19-20/x2)

Full Attack: +27 Claw 1d10+21 (19-20/x2)/+27 Claw 1d10+21 (19-20/x2)/ +22 Bite 1d8+7...

How is this for a rough draft? Any comments on CR or so?

what does his claw do? 1d8 or 1d10. it's different in the attack and the full attack. You don't need to write up both claws, just say 2 claw.
How did he get a damage bonus of +21? str modifier is only +9?

Maybe make his DR only bypassable by weapons that are magic and silver