TEXT:  
  The creature you target must make a wisdom 
  saving throw, and if it succeeds, neither of you 
  are transported to the plane.
   
  In order to shapeshift into a creature you have 
  defeated, you must use your action to transform. 
  You assume the hit points of your new form, and 
  if you revert to your normal form as a bonus 
  action, you return to the number of hit points 
  you had before transforming. If you revert as a 
  result of dropping to 0 hit points, any excess 
  dama
  damage carries over to your normal form. If you 
  shift again without taking a long rest, you 
  assume the hit points you had before reverting. 
  While shifted, you retain your personality, 
  intelligence, wisdom, and charisma. 
   
  If you use this spell again and defeat another 
  creature, you may only shift into the most 
  recently defeated creature.
  Taken from Magic the Gathering
  BoltNine Homebrew
  By Jonoman3000
  
SOURCE: textdata/thevault/Dungeons & Dragons [multi]/5th Edition (5e)/3rd Party/Bolt Nine Homebrew/Final Confrontation.pdf