I'm torn here; there's a strong temptation to make MUTANTOR! another OSR permutation, and stick with the d20 for combat and skill resolution. But if I go my own way here's what I'm thinking of doing.
The MUTANTOR! mechanic would look something like this:
Roll three d6 dice, scratch the highest and lowest roll take the middle dice as your result. Equal or beat the difficulty to succeed.
If you roll Doubles (two dice have the same face), add 1 to that face, that's your result.
If you roll Triples (all dice have the same face) add 2 to that face, that's your result. Plus the dice MUTATE!
For the player that rolled the triple, from now on their dice rolls have MUTATED: anytime that face turns up in following dice rolls it gets treated like a wild die or joker and the player gets to choose what that die should be.
Any mutant dice roll can mutate into a MUTANT Double.
If you roll a natural MUTANT Double it can mutate into MUTANT Triple.
If you roll a natural MUTANT Triple... a MEGA MUTATION or something big and cool and I don't know what yet*.
The MUTANT dice effect lasts until the player uses the dice to form a MUTANT Triple, or they roll a natural MUTANT Triple, or the game session ends.
From what I can tell about the probabilities, it all looks something like this:
chance to roll any particular combination : 1/216 (0.46%)
chance to roll a Double : 90/216 (41.67%)
chance to roll a Triple : 1/36 (2.78%)
chance to roll and mutate into a MUTANT Double : 75/216 (34.72%)
chance to roll and mutate into a MUTANT Triple : 30/216 (13.89%)
chance to roll and mutate into a MEGA MUTATION : 1/216 (0.46%)
*MEGA MUTATION... I'm thinking that the player's dice pool permanently mutates; something like one of their three d6's evolves into a d8. next megamutation the another mutates into a d8 again, til they're rolling three d8s... and then d10s, then d12s, and so on.
So yeah. there you have a it, a straight forwardish dice mechanic that reflects the nature of the game.
I'd really like your thoughts on it, whether it works or has loopholes or can be over exploited or whatever. Cause once the system is locked in then I can get cracking on the rest of MUTANTOR!
Some samples of dice rolls:
Normal rolls: drop the highest and lowest
146 = 4
456 = 5
Doubles: take the double face and add 1
225 = 2+1 = 3
323 = 3+1 = 4
616 = 6+1 = 7
333 = 3+1+1 = 5 AND the dice mutate, with any roll of 3 becoming a Mutant roll
Normal Mutant (where for example 3 is the Mutant)
125 = 2 (no mutations)
Mutant Doubles (3 still the Mutant)
315 = double 5 = 5+1 = 6
Mutant Triples (3 again)
344 = triple 4 = 4+1+1 = 6, and the mutant dice effect ends.
336 = triple 6 = 6+1+1 = 8, and the mutant dice effect ends.
MEGAMUTANT (3 is still the Mutant)
333 = wacky mega effect, and the mutant dice effect ends.