From Dragon Ball Encyclopedia
Cooler uses the Death Flash in his first form by charging the attack with both of his hands upwards and firing it with his one hand.
Cooler uses the Death Flash in his final form by charging the attack with his one hand backwards.
Death Flash appeared in Dragon Ball Z: Cooler's Revenge. Cooler used this attack in his fight against Son Goku in his Super Saiyan form as a diversion to charge his Supernova, with the Death Flash having no effect on Super Saiyan Goku. When Goku fell into the river after being blasted by Cooler, Cooler hunted him and fired his Death Flash at him.