Wishing for other players summons.

[Finalgenesis]

It also has good utility on looting and stopping uniques.

Say they have chalice or whichever artifact you want on the unique unit, you can wish it into your reception party and loot it all. It would should give you better value then wishing for the artifact itself as there should be other goodies on the unit, in addition to depriving the opponent of said unit. Unfortunately it has to be a unit you can specifically target with wish, and you need the intel of where those items are, so it's pretty limiting in that manner...

A good way to stop a Gate-stone unique (targeting restrict applies of course) too, you even have a net gem gain from looting gate stone alone... If it isn't a unit you can target you can wish for the gate-stone and strand him wherever he raid, it wouldn't be too bad a deal either gem wise.