Destroy target permanent an opponent controls. Its controller may search their library for a basic land card, put it onto the battlefield, then shuffle.
(05/10/2018)
If the target permanent is a legal target but isn't destroyed, most likely because it has indestructible, its controller may search their library.
(02/02/2024)
If the target permanent is an illegal target by the time Assassin's Trophy tries to resolve, the spell doesn't resolve. No player searches their library.
(05/10/2018)
If the permanent's controller doesn't search their library, they don't shuffle their library.
(05/10/2018)
If the target permanent is an illegal target by the time Assassin's Trophy tries to resolve, the spell doesn't resolve. No player searches their library.
(02/02/2024)
If the target permanent is a legal target but isn't destroyed, most likely because it has indestructible, its controller may search their library.
(02/02/2024)
If the permanent's controller doesn't search their library, they don't shuffle their library.