A Critical action in games is an action that produces more than the normal result would.
In some roleplaying games a critical hit is when an attack does something devastating to the foe on the opposing end of the blow. To show such a result the damage is multiplied by some value or the damage rolled is maximized instead. Critical hits are usually determined by rolling the highest value in roll over systems or lowest value in roll under systems on the dice used to reach a conclusion. Some abilities may also cause an attack to auto crit, or automatically count as a critical hit.
- If that second roll misses, then it's a regular attack.
- If that second roll hits (it's not necessary to crit again), then the critical hit is accepted as such.
In other kinds of games, critical hits have their own effect tables. These often cause damage to locations or targets usually unable to be directly damaged, or occasionally force Save Or Die effects (sometimes on other targets).
Notable examples include:
- Battletech, where critical hits do nothing most of the time and then blow up your 100-ton Assault mech instantly.
- Mekton, where you have a 1-in-10 chance of forcing a DC1 or DC6 Save vs (Pilot and Mech) Death, or can do other things like instant limb destruction, unavoidable Mech loss or weapon destruction (not as nasty as Battletech, though)
- Dark Heresy, which has the best critical tables bar none. They work more like negative hit points, but a critical hit that makes your damage die explode is a good way to land there. The tables cover people spontaneously projectile vomiting, the chance to slip on the gibs left over from your MONSTER KILL and more. That's just using a lasgun.
- Black Crusade replaces the exploding damage die with an actual "roll on the crit table" mechanic, though it's limited to the lowest five entries.