In 3.5, if you roll a natural 20, or lower for certain weapons, you have a Critical Threat; you have struck a vital area, and can deal large amounts of damage.

Whenever you get a critical threat, you roll again to confirm your success against the same AC. If you succeed, your damage is multiplied based on the weapon, usually x2.

In 3.6, you also get a bonus effect based on a d12 for location and d6 for effect, off our crit table. Also in 3.6: if you roll a 20 on both the original roll, and the confirm roll, you get a double crit: the damage is multiplied by the crit mod twice. Aka x2, then x2 again. If you roll 3 20s in a row, the target is instantly killed by the attack.

In 3.5 if you roll a natural 1 on any check you cannot add any bonus and it is a catastrophic failure, typically leading to a setback in the effort. In 3.6 you can also use this table to determine what sort of setback you face if you roll a natural 1 in combat.

To Determine which Body Part is Struck

d12 Result	Body Region
1	Right Lower Leg
2	Left Lower Leg
3	Right Upper Leg
4	Left Upper Leg
5	Left Upper Arm
6	Right Upper Arm
7	Left Lower Arm
8	Right Lower Arm
9	Abdomen
10	Chest
11	Neck
12	Head

To Determine the Effect on the Struck Body Part

Location chosen- d6	Slashing	Piercing	Bludgeoning	Energy
d6 Result-Lower Leg	Can sever foot at 1/5
1	Item in area takes same damage	>	>	>
2	Normal Critical Mod	>	>	>
3	Ankle Damage: Half Speed, 1d4 Dex	>	>	>
4	Achilles: 1/4 Speed	Nailed Down: Immobilized, Bonus Attack	Shinshatter: 1d8 Dex	>
5	Swept Leg: Knock Prone	>	>	>
6	Foot Damage: Half Speed, 1d6 Dex Damage	>	>	>
d6 Result- Upper Leg	Can sever leg at 1/4
1	Item in area takes same damage	>	>	>
2	Normal Critical Mod	>	>	>
3	Knee Damage: Half speed, 1d4 Str	>	>	>
4	Hamstring: 1/4 speed	>	Kneecap: 1d4 Str, 1d4 Dex	>
5	Hammer: 10' knockback	>	>	>
6	Bloody Wound: 2d4 Bleed	>	Shattered Pelvis: 1d6 Dex, 1d4 Con	Nerve Damage: 1d4 Wis, 1d4 Dex
d6 Result-Upper Arm	Can sever arm at 1/4
1	Item in area takes same damage	>	>	>
2	Normal Critical Mod	>	>	>
3	Elbow Damage: 1d6 Str	>	>	>
4	Shatter Bone: 1d6 Str, 1d6 Dex	>	>	>
5	Shoulder Damage: 1d8 Str	>	>	>
6	Cleft Collar: 1d8 Str, Fatigue 1d6 rounds	Rending Stab: 3d8 Bonus Damage	Crush Collar: 1d8 Str, 1d4 Con	Nerve Damage: 1d4 Wis, 1d4 Dex
d6 Result-Lower Arm	Can sever hand at 1/5
1	Item in area takes same damage	>	>	>
2	Normal Critical Mod	>	>	>
3	Finger Damage: 1d4 Dex (1/8 sever)	>	>	>
4	Slash Wrist: 2d4 Bleed	>	Crush Hand: 1d6 Dex	Extreme Pain: Nauseated 1d4 Rounds
5	Elbow Damage: 1d6 Str	>	>	>
6	Slash Away: Disarm	Nailed: Hand Immobilized, Bonus Attack	Shatter Wrist: 1d4 Dex, 1d4 Str	Blow Away: Disarm
d6 Result-Abdomen
1	Item in area takes same damage	>	>	>
2	Normal Critical Mod	>	>	>
3	Eviscerate: 1d3 Con Damage	>	Spine Damage: +1 Crit Mod	Visceral Shock: Nauseated 2d4 Rounds
4	Groin Damage: Stagger 2d6 rounds	>	>	>
5	Disemboweled: 2d4 Bleed	Skewered: Entangled, Bonus Attack	Gut Punch: Nauseated 2d4 Rounds	Organ Burst: 2d4 Bleed Damage
6	Spine Damage: Paralyze 1d6 rounds	>	>	>
d6 Result-Chest
1	Item in area takes same damage	>	>	>
2	Normal Critical Mod	>	>	>
3	Wicked Gash- 1d3 Con Damage	Heart Stab: +1 Crit Mod	Broken Ribs: Fatigued	Heart Stutter: Dazed 1d4 rounds
4	Wedged- Bonus attack to pull out	Punctured Lung: 1d3 Str, Fatigued	Walloped: Knocked Prone	Lung Damage- 1d3 Str, Fatigued
5	Bloody Wound- 1d6 Bleed	>	Broken Collarbone: 1d6 Str	Lingering Energy- 1d6 lingering damage
6	Slit Muscle: 1d6 Str damage	Run Through: Entangled, Bonus attack	Kidneys Bruised: Nauseated 1d6 rounds	Blast Back: 10' knockback
d6 Result-Neck	Full HP can sever
1	Item in area takes same damage	>	>	>
2	Normal Critical Mod	>	>	>
3	Throat Cut: +1 Crit Mod	Impaled- Bonus attack to pull out	Broken Neck- 1d6 Dex Damage	Nerve Damage- 1d6 Dex Damage
4	Bloody Wound- 2d6 Bleed Damage	Bloody Wound- 1d6 Bleed damage	>	>
5	Windpipe Damage- Muted, Suffocation	>	>	>
6	Nerve Damage: 1d4 Wis, 1d4 Dex	>	Crushed Throat: Fatigue 1d6 min	>
d6 Result-Head	Eyes+Ears take 1/8 health to destroy
1	Item in area takes same damage	>	>	>
2	Normal Critical Mod	>	>	>
3	Split Skull- 1d4 Int Damage	Headshot: +1 Crit Mod	Head Crushed: +1 Crit Mod	Ears Burst- Deafened 1d6 rounds
4	Facial Damage- 1d4 Cha Damage	>	>	>
5	Eye Slash- Blinded 1d6 minutes	Eyeshot- Blind 1d6 rounds, +1 Mod	Concussion: 1d4 Int Damage, Confused 1d6 round	Eyes Damaged- Blind 1d6 min
6	Jaw Chop- Muted 1d6 minutes	Lobe Damage- 1d3 Int, Wis Damage	Knocked Loose: Stunned 1d4 rounds	Overwhelmed- 1d6 Wis damage, Dazzled 1d6 rounds