I faced a similar ogre army recently. Hordes of Bloodletters leaping fowards took the majority of the fire power, he thought the Lord of Change wasnt a priority since it wasnt that beat stick in combat... that was until it flew down the flank and unleashed a full blown "Purple Sun" down his literal line.
Lets just say by the end of that spell i had max power dice from the lore attribute and the rest of the game didnt go to well for him.
Don't, after rolling that final 1 too many, flip out, climb up on the table and jump up and down on your opponent's models screaming 'APOCALYPTIC BARRAGE, MOTHERFUCKER!!!'.