EX Skill

EX Skill (EXスキル) is a system from the Mega Man Zero series.

Zero
The EX Skill system was introduced in Mega Man Zero 2. When Zero defeats a boss while having rank A or S (or with a weather favourable to the boss in Mega Man Zero 4), Zero will gain a new ability that can be used with his weapons.

Bosses
The name EX Skill also refers to the extra attack used by bosses when Zero fights against them with a Rank A or higher, such as Aztec Falcon's Lightning Fall and Hyleg Ourobockle's Joint Laser.