Sorry to say but the only interesting aspect of an IP is the Lore and Fluff. Most tabletop Rules need a GM which a PC doenst have and with so much Compute Power you can simulate original rules without use them. I cant use a d20 system? Behold my d21-1 dice!
I see your d21 -1 die, and raise you a system where it's contested die rolls/dice rolls with a die that WotC can't claim any type of ownership over, a d6. Player A is attacking Mob B, Player A rolls 2 d6, Mob B rolls 2 d6. Highest roll wins.
