A transformation item is an item that otherwise changes the appearance of your current player character via use by an item, such cases are like Noggenfogger Elixir or Orb of the Sin'dorei. These items do not affect your character's combat skills but is mainly used for cosmetic appearance and for entertainment, some use these items for Roleplaying in disguise or otherwise for other uses.
There are 2 types, those consumed by use and those that aren't, below is a few that are consumed by use or multiple uses: Orb of the Blackwhelp- 2 charges, turns the player into a black whelp, you cannot cast spells or attack within this form. Noggenfogger Elixir- (Charges depend on quantity) Transforms you into a Skeleton or shrinks you or gives you a gliding effect when going off places where you would otherwise fall. Or all three at once.