Critical hit

In many role-playing games and video games, a critical hit (or crit) is a successful attack that deals more damage than a normal blow.

The 1975 role-playing game Empire of the Petal Throne introduced the concept of critical hits (though not the phrase). Using these rules a player who rolls a 20 on a 20 sided die does double the normal damage, and a 20 followed by a 19 or 20 counts as a killing blow. According to creator M.A.R. Barker, "this simulates the 'lucky hit' on a vital organ."

Critical hits are meant to simulate an occasional "lucky hit". The concept represents the effect of hitting an artery, or finding a weak point, such as a stab merely in the leg causing less damage than a stab in the Achilles tendon. Critical hits are almost always random, although character attributes or situational modifiers may come into play. For example, games in which the player characters have a "Luck" attribute will often base the likelihood of critical hits occurring on this statistic: a character with high Luck will deal a higher percentage of critical hits, while a character with low Luck may, in some games, be struck by more critical hits. In the role playing game Dungeons & Dragons, when a player character attacks an opponent the player typically rolls a 20-sided die; a roll of 20 (a 5% chance) results in a critical hit.

The most common kind of critical hit simply deals additional damage, most commonly dealing double the normal damage that would have been dealt, but many other formulas exist as well (such as ignoring defense of the target or always awarding the maximum possible damage). Critical hits also occasionally do "special damage" to represent the effects of specific wounds (for example, losing use of an arm or eye, or being reduced to a limp). Critical hits usually occur only with normal weapon attacks, but not with magic or other special abilities.

Many table-top and video games use "ablative" hit point systems. That is, wounded characters often have no game differences from unwounded characters other than a reduction in hit points. Critical hits originally provided a way to simulate wounds to a specific part of the body. These systems usually use lookup charts and other mechanics to determine which wound was inflicted. In RPGs with non-humanoid characters or monsters, unlikely or bizarre results could occur, such as a Beholder with a "lost leg". Most systems now simply award extra damage on a critical hit, trading realism for ease of play. The effect of a critical hit is to break up the monotony of a battle with high, unusual results.

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Wikipedia