A power which was suggested to me by Koewn for my Geckomen is a detachable tail.
Sacrificing the tail will make the Geckoman completely avoid a roll on the Mortal Wounds table. HOWEVER, a tail is important to a Geckoman’s health, as well as balance, and as long as he is tail-less, he will suffer a -2 penalty to his Dexterity and Constitution scores (if either of these scores is reduced to zero by this, the Geckoman must roll on the Mortal Wounds table anyway) until the tail regrows. Regeneration takes 3d3 months.
I’d call that too powerful, personally, though I like the idea. If you keep the idea that the mortal wounds table d6 roll is a hit location, then let the appropriate location for body or legs count as tail here (both or choose which looks more appropriate).
Have losing the tail give a big bonus to the roll, like +10 or even +20, and it suddenly seems close to a 1-2 proficiency power to me, rather than a free life.
Alternatively, let it reduce one hit down to 4 HP at the cost of a tail, if the goal is to let them lose it and keep fighting, or something.