Well, I'd just have to say that you should probably drop the "Devour" aspect, because when it comes to % chance, you either insta-kill, or drain the power from it. Since insta-kill is a no-no, you'll have to settle with the alternative.
"Gouge: 50% chance to gain +3|+3. Target creature gains -3|-3. If this kills target creature, add 5% to Gouge chance"
Capiece?