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At the end of the next turn, the Pokemon at the user's position has 1/2 of the user's maximum HP restored to it, rounded half up. Fails if this move is already in effect for the user's position.
Wish is not the move it used to be in previous generations, and must be looked at from a different perspective when choosing what Pokemon should use it. In previous generations, any Pokemon with access to Wish could be used as a Wish passer since the move healed 50% of the recipient's HP. With the BW mechanics, however, where Wish only heals 50% of the user's HP, it requires a high base stat, so Pokemon such as Chansey and Blissey are even better Wish passers than they used to be, while others like Espeon no longer are useful.
Wish is one of the best support moves available though its limited distribution means that fitting a Wish user onto a team might not be easy. Wish provides recovery to the user and its teammates. It can give teammates that do not have other means of recovery a second life or even more. This can also save a moveslot on a teammate if it can opt not to use a recovery move it already has access to. However, Wish can be intercepted if the supposed recipient faints before Wish activates on the second turn, making Wish rather hard or impossible to use at times. The two turns required for Wish to take effect can also be made use of by the opponent; the opponent can make use of these two turns to knock out the Wish user or the recipient, or even set up. Wish is helpful in offsetting entry hazard damage as well in a scenario whereby the receiver switches in to heal with Wish but takes entry hazard damage in the process of doing so. Wish is an invaluable support move despite it not being completely reliable occasionally.