Watcher

{9}{b}{b}{b}{b}{u}{u}{u}{u}, transform Watcher
into a legendary artifact creature. Transform
Watcher for free is you've cast 5 or more
creatures with 8 or more power this game.

When Watcher attacks, target player must search
their library for three non-legendary creatures, place
them on the bottom of their library, and then exile
the rest of their library.