Critical Hits and Misses
When rolling d20 for attacks (or, occasionally, skill checks), "naturally rolled" (before any +/- modifiers are taken into account) 20s and 1s are considered Critical Hits and Critical Misses, respectively.
On attack rolls, Critical Hits always succeed regardless of target AC; Critical Misses always fail regardless of target AC.
Critical Hits represent spectacular successes and good luck. Conversely, Critical Misses represent terrible failures and bad luck.
When a Critical Hit occurs, damage is doubled and the PC is rewarded with a second d20 roll. If this is also a Critical Hit, then damage is tripled. Repeat until a non-20 is rolled. Roll an extra die of damage for each consecutively rolled Critical Hit (e.g., 1d6+2 DMG would be rolled as 2d6+2 ).
*DO NOT roll damage and then multiply result by 2. Do NOT double any +/- modifiers.*
# of Consecutive Critical Hits (aka "Natural 20s") Damage Dice Multiplier
1 2dx+y
2 3dx+y
3 4dx+y
4 5dx+y