Comment on Lyra Learns Dark Magic by T-3000
Everyone says it's dark magic, but I think it is an illusion spell. Still, it seems to work for demanding stuff. 
It's obviously not an illusion spell. It clearly changes the Crystal Castle into its "evil" state like it was under Sombra, powers up the Nightmare Door, and besides, Sombra's horn glows like that whenever he casts a spell and I'm pretty damn sure he doesn't use illusions.