That's not true. It's completely random, with a higher chance on harder difficulties I think. It'll have a set condition like Nightmare!-only or YAAM-only soon-ish (maybe)
Not true. Current conditions are: YAAMed everything up to UC, 50% chance on HMP, 60% on UV. Confirmed by KK and add, so true. Changed to guaranteed if above conditions are met in Beta 3 or 2.