The blue bar under your Hero's Health is the Rage bar. When full, click your hero so they can perform their ultimate ability (1st skill). Rage carries over between waves (not in Trials) and the Gauntlet but not stages or levels.
Rage bar is full when you get a total of 1000 Rage.
How a Hero gains Rage
- Suffering damage gives a variable amount of rage depending on percentage of health lost compared to max health pool
- Any action done by a hero gives a fixed amount of rage (30?)
- Rage Regen grants rage after each wave in Crusade (normal difficulty) and Campaign battles.
- Prometheus' 2nd skill "Bad Buddy" restores rage to a random friendly unit
- Dealing a killing blow gives 300 rage
How a Hero loses Rage
- Using your Hero's Active ultimate skill
- Astraea's 3rd skill "Condemnation" targets Front and Mid Heroes. Rage lost based on the skill's level.
- Medusa's 3rd skill "Siphon Rage" steals a flat amount of Rage from all heroes hit. Rage lost based on the skill's level.