The ultimate life form is liquid. Not a specific liquid, but to become the very concept of liquid itself. You can't punch liquid, you can't shoot liquid, you can't stomp on liquid, and it just comes back when it evaporates in the form of rain. Helmet can't be shot, he can't be hurt, and he can only be temporarily contained in that liquid state. Even Kars from Jojo would be in awe of the sheer brilliance of this path of evolution.