Kithysda, the Iron Dawn

Reach
As long as there are less than three Legendary Creatures on the battlefield, Kithysda gains Indestructible and Protection from instants and sorceries.
When more than three Legendary Creatures are
on the battlefield, Sacrifice Kithysda and search
your library for up to three instants or sorceries,
you may cast them this turn for {1}.