Cool video to see how the new hero is working for you. But he does not negate Celeste cursed flame. Celeste dies in that clip just before her flame went out from switching to dark form. As far as I know, no one cleans up the field from the ground effect that Celeste nor other heroes place. They can weaken the effect, but not remove it. You can, however, remove debuffs. Like Celeste limbo (blue skill) and Nebula Serenity (green skill) can remove stacks of fox fire that Satori places or marks of water that Krista places. But nothing that Sebastian does removes the field effect of dark flame. Hope this helps.