Thought Projection

Thought Projection (思念体 Shinentai) is a Caster Type illusion Magic.

Description
The user separates his maximum supply of Magic to create a mental copy of himself or anybody else.

Jellal introducted his copy Siegrain. Jellal and Siegrain can travel great distance apart from each other and still transfer information between themselves. Since Siegrain is not really a physical being, he can also appear and disappear across great distances, although he can still interact with physical objects. The quality of Jellal's copy is enough to fool S-Class Mages like Erza and even the entire Magic Council. Once Jellal and Siegrain reunite, Jellal's Magical capacity returns to normal.

Roubaul generated many people by his will. Not only can his illusions have their own emotion and personality, but they can take a physical form and do actual life-like actions. In addition Roubaul's illusions are self-sustainable (unless by their own will to go or ultimately by Roubaul's will). Another possibility is that his Magical capacity is so vast, that he alone is keeping everything intact for seven years straight. This might also explain why only Wendy and Charle were the only ones to go on the mission. However, due to Nirvit's background of being neutral, it's most likely that his illusions are not meant to be destructive, which explains why he can't destroy Nirvana himself. It is currently unknown if his illusions can be considered living beings.