Mega Froslass

She changes and reveals a ghostly body with another set of arms similar to those of Haunter. Her dress transfers up into a cloak-like pony tail with the bow holding it together. She grows an Ice crown, Ice razors on her sleeve-like arms, and an ice diamond on her ghostly "chest." 

The cool thing about this mega transformation is that now, Froslass can divide into a complete Ice-type and a complete ghost-type by splitting away from her ghost body. This is her special abilities known as "cursed body" and "snow cloak" taken to a whole new level!  

This also allows her Mega form to know a total of 8 moves when split, and cheats events of only having a certain number of pokemon. The downside of her transformation is that once one part of her faints, the other is soon to follow.

I hope you like my concept!