The user transforms into a copy of the target right down to having the same move set.
User copies the target's species, weight, type, ability, calculated stats (except HP), and moves. Copied moves will all have 5 PP remaining. IVs are copied for the purposes of Hidden Power, but stats are not recalculated.
Choice Band, Choice Scarf, and Choice Specs stay in effect, and the user must select a new move.