Moody

Moody is a volatile ability introduced in Generation V that randomly raises one of the Pokemon's stats by two stages and lowers another by one stage at the end of each turn. This creates a net gain of one stage per turn, meaning a Moody user will become progressively more dangerous the longer it stays on the field.

The stat selection is truly random among the seven battle stats (Attack, Defense, Special Attack, Special Defense, Speed, Accuracy, and Evasion). A stat already at +6 cannot be chosen for the boost, and a stat at -6 cannot be chosen for the drop, which concentrates the changes on remaining stats over time. In Generation VIII, Accuracy and Evasion were removed from the pool of eligible stats, reducing the RNG frustration that made Moody controversial.

Moody is widely considered one of the most luck-dependent abilities in competitive play. Pokemon like Glalie and Bibarel have occasionally seen use in lower tiers specifically because Moody can snowball games -- a lucky Speed or Evasion boost combined with Protect or Substitute stalling can make the user nearly untouchable. Many competitive formats have debated or restricted Moody and evasion-boosting combinations due to their uncompetitive nature. The ability is found on 8 Pokemon.