Long ago and far away, I rather "inherited" the duty of working with/on a homebrew RPG system on a MU* (which here, is a word that means 'online text-based RPG with a persistent environment'). The original designers were a bit notorious for not clearly defining what certain supernatural tricks could do, and I've slowly been trying to fill in those gaps.
Some weren't so bad. I could ask "For those of you with Undefined Power X, or who have had a character with Undefined Power X in the past, could you let me know what level you had it at and what tricks your characters did with it?" now and again and then retrofit a system mechanic to allow folks to do what they'd done in the past, yet have something cohesive for new players.
The one that's stymied me is Regeneration. For some alien reason, there's both Healing (which is healing what one could normally mundanely heal, but in a far shorter amount of time) and Regeneration (which is healing normally unhealable things, like replacing severed limbs or incidents that would require plastic surgery or skin grafts to fix). Alas, combat doesn't happen all that often in the game so there isn't much of a case history to work off of.
Obviously, the easiest answer would be to ditch Regeneration as a stat, make it part of Healing, and then offer folks a rebate for any points dropped into Regeneration, but I've always liked a challenge. My initial instinct was to try to ferret up some charts about newts and stem cells and things and the actual regeneration rates so I could adapt that, but so far nothing's really turned up that provides useful data.
Is anyone out there familiar with some RPG that has a Regeneration system mechanic that I could pilfer and adapt?
I already have it being factored into "How long does it take for your character to heal X points of damage?" formuli, but what I'm lacking is a more qualified, "How long does it take for that arm/eye/tooth/appendix/ear to grow back?" layout.