In the notes, you should describe the exact percentages.
Balance-wise, it's hard to consider, because granting a random ability doesn't seem like a mechanic worth a card slot. The insta-kill mitigates some of that as you can now use it as CC, but that's not a good direction to go towards.
Thematically, it is very very similar to mutation, and fits
the best. Of course, then you have to make sure it doesn't overshadow (or get overshadowed by) mutation.