Critical Hits are a recurring feature of the Dragon Quest series.
Every time any character makes an attack, they have a small chance of that attack being a "Critical Hit," which drastically increases the damage dealt on that particular turn. Since critical hits ignore defence, it makes them an instant kill on all metal monsters, provided the monster does not dodge the critical hit. However, many monsters also can get critical hits, usually termed a terrific blow or a brutal hit.
The chance of a critical has several variables, though the base range in all Dragon Quest games is 1⁄64. Certain characters have a better chance of getting critical hits than others, such as Tsarevna Alena whose rate depends on her level. In VI and VII, a Martial Artist's chance of landing a critical hit improves along with the character's current rank, capping at 1/8 at rank 8.
Certain weapons can increase the chances of a character getting a critical hit, such as the Hela hammer or Headman's Axe. Such weapons tend to have a very low accuracy to balance their power. Additionally, weapon skill sets featured in Dragon Quest VIII and IX will improve a character's chances of performing a critical hit from 1⁄64 to 1⁄32 if they raise their rank in the skill high enough.
In Dragon Quest IX, spells can also become critical hits, where the spell "goes haywire." This not only increases damage output of attack magic, but also boosts healing spells. If a status-changing spell goes haywire, its chance of working increases to 100% (barring the target being immune). Other class skills have a critical chance as well with similar effects.