This is the "if they had called me" version of Mandrakes. They never will, but hey, here is my half cent opinion.
Keep everything they upgraded about them as is. Change their point cost to 25pts per model and give them a new ability called Shadow Jump. During their movement phase, if a unit of Mandrakes is in, or partially in area terrain, they may instead of moving, select a spot within 24" (it is possible to scatter beyond the 24" range) that is also inside area terrain. They may jump to this location. Roll the scatter dice as if they are deepstriking and move them to this new location. If a "hit" is rolled, the mandrakes may now assault the round they jumped. Note that any model that cannot appear due to impassible terrain or another unit are lost to the shadows and removed from play.