Myra, Mistress of Time

When Myra, Mistress of Time enters the battlefield, you may search your library for up to
four instant or sorcery cards, reveal them, put
them into your hand, then shuffle your library.
Whenever you play an instant or sorcery spell, if
it's the fourth instant or sorcery spell you've cast
this turn, exile Myra, then return her to the battlefield transformed under her owner's
control.