Defense Up
From Inkipedia, the Splatoon wiki
Defense Up reduces damage taken from all attacks by up to 20%. Unlike Damage Up, it can lower thresholds on enemy weapons. For example, the .52 Gal does 52 base damage, which is a two-shot splat. Defense Up can drop the weapon below 50 damage, making it a three-shot splat with the .52 Gal. This is one of the most valuable abilities, particularly if you're new to the game, decreasing the effectiveness of your opponent's weapons. Players with an aggressive play style can also benefit from Defense Up.
In-Depth Ability
Use
Gear
Defense Up is the main ability of:
