Katia's once-a-day battering-ram charge — unpredictable in distance and aim — that accidentally kills Hekla.
Rush is Katia Grim's doppelganger charge skill: it turns her body into a battering ram that blasts forward and shatters everything in its path. She hates using it — Mordecai pushes her to lean on it, but it knocks the wind clean out of her even on a miss, is limited to once a day, and is maddeningly unpredictable, hurling her anywhere from five to twenty feet and sometimes veering off-center. That unpredictability turns fateful in the gore-flooded train cab: enraged by Eva's cruel taunting after Hekla's betrayal, Katia screams and Rushes at Eva — misses her by inches — and instead splatters Hekla, the #2 crawler, against the train wall, becoming the season's first crawler to kill a top-ten and claim a 500,000-gold bounty (and a golden skull), rocketing from level 24 to 37 in an instant.
A doppelganger skill: Katia's body compacting and launching forward as an unstoppable ram, shattering whatever it strikes.
Katia's signature charge attack, whose erratic aim accidentally kills Hekla and transforms Katia's power.
Also appears in books you've already read — spoiler-safe to their endings: