The problem with minions is, her breakdown in canon lasted about half an hour - she brought about an eclipse, turned into Nightmare Moon, demolished half the castle while trying to shoot her sister, then Celestia picked herself up from the ground, took the elements of harmony out of storage and sealed her.
The nightmare creatures from the comic would be her minions (along with their boss Larry... I mean Shadowfright)
Powers: besides messing up the day-night cycle ( "The night will last FOREVER!" ), she has weather control at will, including hitting opponents with lightning from available clouds. She also shoots generic energy beams. Can shapeshift and travel as a cloud of darkness, but is otherwise material - you can do physical damage to her if you catch her off guard.
Finally, later episode established that Luna herself can travel through dreams. She uses this ability to defend her subjects from nightmares (popping into their dream and zapping whatever is scaring them) but if she were to turn evil, she could really earn her name (this is also how the nightmare creatures began their attack on Ponyville)