Kahoi. ScrollStocker Mage

Whenever an instant or sorcery you control is sent to your graveyard after you played it this turn, you may pay {u}{u}. If you do, have Kahoi exile it. Then put a scroll counter on Kahoi.
{6}{u}{u}, {t}: Exile Kahoi. You may play any number of instant or sorcery spells exiled by Kahoi without paying their mana costs this turn. Then exile those spells. If you have 8 or more scroll counters on Kahoi, shuffle Kahoi into your library instead of exiling it.