Sakashima the Impostor | Opalescence | Detention Sphere

Cards

Cast
Sakashima the Impostor by paying ({2} magic symbol) ({U} magic symbol) ({U} magic symbol) , having it enter the battlefield as a copy of
Detention Sphere that is a 3/3 legendary enchantment creature named Sakishima the Imposter.
When
Sakashima the Impostor, it triggers its first ability from
Detention Sphere, exiling itself.
Sakashima the Impostor leaves the battlefield, triggering its second ability from
Detention Sphere, returning itself to the battlefield as a copy of
Detention Sphere that is a 3/3 legendary creature named
Sakashima the Impostor.
Repeat from step 2 any number of times.
End the loop by choosing a different creature to copy or a different permanent to exile, or by declining to exile anything.