Oath of Bookner

When Oath of Bookner enters the battlefield,
draw four card, then discard four cards.
Whenever you activate a loyalty ability of a planeswalker you control, search your library for
a noncreature spell with converted mana cost
equal to or less than the number of planeswalkers
you control and put it into your hand, then
shuffle.
For the preservation of ancient lore, I will keep watch.