Rebellion Gauge
The Rebellion Gauge is a mechanic unique to Joker in Super Smash Bros. Ultimate.
Overview
The Rebellion Gauge is a gray meter with a black frame and a red splash around it, which is present next to Joker's portrait at all times. As the Rebellion Gauge fills, the gray is replaced with pink.
The Rebellion Gauge slowly fills over time, but can be more efficiently filled by (in order of effectiveness) attacking opponents, being attacked (which causes a red spark at the right end of the Gauge), and being attacked while using Rebel's Guard. When the meter is filled, Arsene is summoned and the Rebellion Gauge turns cyan with blue flames behind it.
Arsene remains active to boost Joker's abilities until the Rebellion Gauge runs out. The meter slowly depletes over time, and taking damage causes larger portions to be removed. Once the Rebellion Gauge depletes fully, Arsene leaves Joker and the meter resets to its default state.
If Joker dies at any point, the Rebellion Gauge is reset to roughly 20% full. This includes if his meter is below that level.
If Joker's shield is broken while Arsene is active, Arsene temporarily vanishes and the Rebellion Gauge stops depleting until Joker leaves his stunned state.