Well you can give the item a ability, for example endurance item ability so it makes you quicker, but make the Stats-Targets Allowed- Self, and if you want the model to show you put your model in teh endurance ability at
Art-Target- (Your Model)
Art-Target Attachment Point 1- origin (or for others
http://www.hiveworkshop.com/forums/general-mapping-tutorials-278/how-to-attach-a-model-or-an-effect-to-a-unit-7314/ )
And for making the unit taller we will use triggers
Event-Unit- a unit Acquires an item
Condition-((Triggering unit) is a Hero) Equal to True
((Item-Type of(Item being manipulated)) Equal to (Your Item)
Action- Animation- Change (Triggering unit) flying height to (How High he will go) at (How fast he will go that high
Event-Unit- a unit Loses an item
Condition-((Triggering unit) is a Hero) Equal to True
((Item-Type of(Item being manipulated)) Equal to (Your Item)
Action- Animation- Change (Triggering unit) flying height to (How Low he will go) at (How fast he will go that Low