20 classified as an automatic hit/succeed,
If you would naturally hit them with a twenty does Critical Damage/Success
If you would not naturally hit them (20+1 < 23AC) you must roll 2 twenties in a row to do Critical damage
Regardless if you roll three twenties in a row it is an instant kill/success,


1 classified as an automatic miss/failure
Must succeed on DC 20 Reflex Save or Critically Fumble
Critical Fumbles include:
Injuring yourself/teammate
Damaging items


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