I sent the following to my players. We're running B/X D&D with a bunch of house rules, this is a proposal for another.
Crits & Fumbles
Rolling a 20 or a 1 should be exciting, but not debilitating or unbalancing
A 20 used to be a critical hit at nearly every table I ever played or DMed. A critical hit was usually double damage, sometimes just multiplying the damage die rolled by two, usually at my table it was roll twice the number of damage dice, adding bonuses for Strength or whatever after.
Since we started using penetration damage I have been leery of adding another bonus, and these affect player characters more often that they affect NPC or Monster combatants.
Likewise a 1 was often a fumble, or at least some sort of fumble check. Sometimes these were funny, sometimes inconvenient, sometimes downright deadly.
However, I'd like to bring back a little of the excitement of rolling a 20 to hit, and the dread of rolling a 1, so I am presenting for possible inclusion into the house rules these simple Crit/Fumbles.
Melee Critical Hits – roll 1d10
1-3 Enemy pushed back, usually 5 feet, into an unoccupied square.
4-5 Enemy knocked prone*.
6-7 Enemy disarmed, enemy drops weapon, which flies 0-15 feet (in 5' increments) in a random direction.
8-9 Enemy shield damaged/destroyed, enemy loses 1 point of AC.
10 - Enemy takes double damage (twice as many dice)
Ranged Critical Hits – roll 1d8
1-3 Enemy drops weapon/shield (50/50)
4-6 Enemy takes double damage (twice as many dice)
7-8 Enemy takes triple damage (thrice as many dice)
Ranged critical hits are clearly harder to give more variety of results to, but I think adding triple damage as a possibility makes sense given that missile weapons are all piercing (even blunt ones like sling stones/bullets); I mean, if it comes down to it and you throw a rock or a brick or something, we can justify the additional damage somehow or ignore any results saying triple damage.
Melee Fumbles roll 1d10
1 - Timing Off - -2 to next initiative
2 - Timing Really Off – lose all actions next round
3 - Off Balance -1 to initiative and -1 to hit next round.
4 - Really Off Balance – Make Saving Throw vs. Paralysis or trip and fall prone*.
5 - Opened Yourself Up -1 to AC until your next round
6 - Really Opened Yourself Up – -1 to AC and nearest enemy gets an immediate free attack.
7 - Butterfingers – Make Saving Throw vs. Paralysis or drop weapon, which flies 0-15 feet (in 5' increments) in a random direction.
8 - OOPS - Accidentally strike nearest ally for full damage, no to hit roll needed.
9 - Break weapon – You broke your weapon. Magic weapons get a saving throw vs. crushing blow, all others just break.
10 - Hit Self – Somehow you managed to hit yourself for full damage.
*Prone characters are at +3 to hit and require their next round to stand up.
Ranged Fumbles roll 1d
1-3 - Dropped weapon – Make Saving Throw vs. Paralysis or drop weapon, which flies 0-15 feet (in 5' increments) in a random direction.
4-5 - Dropped Ammo – lose next round retrieving ammo, if using a thrown weapon treat as dropped weapon.
6 - Broke Weapon - You broke your weapon. Magic weapons get a saving throw vs. crushing blow, all others just break. Exception – bows and crossbows only break the string on a 1-5 on a d6.
7 - Hit Ally – missile strikes ally nearest to intended target for full damage, no to hit roll required.
8 - Hit Self – Somehow you managed to hit yourself for full damage.
I agonized over whether ranged weapons should just use the melee fumble table, and whether thrown weapons needed to be separated from bows and other launcher based weapons, but opted for the middle ground here. There's room for discussion in any case.