Critical hits and Dungeons & Dragons have a long, if largely unofficial history. Most DMs have put together their own critical hit tables and fumble tables, or at least have borrowed from some of the many tables that have found their way into old issues of Dragon Magazine, Rolemaster or other games.
Most of those tables rely upon a to hit roll being a natural 20 (or a natural one for fumbles). Which basically means a fighter that almost always can hit has a small percentage of crits, and a large number of his misses are fumbles. Something about that just doesn't seem fair.
My solution, or at least, what I'll be experimenting with in my next Labyrinth Lord game, is the use of a control die. I may us a d10, or even the lonely and rarely used d12. Roll maximum on the control die when you score a hit with the d20 and you've scored a crit... miss when you roll a 1 on the control die and you've scored a fumble.
As for the effect of a critical hit or a fumble, choose you favorite tables or use the maximum damage for crit, attack lost next round for the fumble. You can even make the control die open ended if you wish, adding damage or negative effects as warranted.
Sandy Petersen's Cthulhu Mythos & Ghoul Island - Now i have used the Cthulhu Mythos since early 80s where friend had the deities book with them which got me a bit late...
33 minutes ago