The Mastery system is a gameplay mechanic introduced in Gungnir. When a unit uses the same weapon repeatedly, they will accumulate Mastery, which will increase their attack power with that weapon. The Mastery value increases by 1 each time an action is performed with the weapon, which caps at 50. Increasing the Mastery level can also pave the way to learning new skills.

Mastery can be seen as a kind of successor to Riviera's Skill Up system.