Musketeer's Mastery

Whenever your commander attacks and isn't
blocked, put a mastery counter on Musketeer's
Mastery.
{1}, {t}: Search your library for an instant or
sorcery card with converted mana cost X or less,
where X is the number of mastery counters on Musketeer's Mastery, reveal it, put it into your
hand, then shuffle your library. When your
commander leaves the battlefield, remove all
mastery counters from Musketeer's Mastery.