As what I've known, Mirajane has only 3 forms :
- Satan Soul
I wonder if how many demon forms does Mirajane have (not yet discovered)? Is it three forms only?
According to Mashima, says that there are 72 demon forms of Mirajane, but It was not yet revealed in manga and anime,
Mashima has went an interesting way with Mira's powers.
Though if you know about demons from the Goetia list or other animes you probably already sort of know.
Lisanna has things like Animal Soul: Rabbit, Animal Soul: Tigress
Elfman has Beast Soul: Weretiger, Beast Soul: Lizardman
Animals and Beasts.
Though in Mira's case of course she'll have demons for her forms, and Mashima has decided to get them from the Ars Goetia list.
So it'd look like for her, Satan Soul: Sitri, Satan Soul: Eligos etc.
Here's the list of demons:
King Baal (bael)
I've read some information about the Mirajane's Take Over magic:
Macro (命令, マクロ Makuro): Unable to fully take over an Etherious, Mirajane took over Sayla's Curse, allowing her absolute control over something, from inanimate objects to even people. She uses this to command Elfman to come to where she and Lisanna are.
For now, she had 3 demon take over. She wasn't able to take over an Etherios where she fought Layla. This is where Layla's true form reveal.