That reminds me, I feel red should explore the space of exiling from the graveyard more, both as costs and effects.
Garbage Fire - 3R
Instant
Exile all cards from target player's graveyard. For every three cards exiled this way, deal 1 damage to that player and add R to your mana pool.
Squalid Pickings - R
Sorcery
Exile up to two target cards from a single graveyard. For each land card exiled this way, add R to your mana pool. For each nonland creature card exiled this way, put a 1/1 red Goblin token on the battlefield. For each nonland noncreature card exiled this way, deal 1 damage to each creature you don't control.
Hopeful Lavamancer - R
Creature - Human Shaman
R, Tap, Exile two cards from your graveyard: Exile the top card of your library. Until end of turn, you may play that card from exile.
1/1
I also feel like exiling from an opponent's library is space red should explore. Milling + an effect based on what was milled (other than more milling) really hasn't been explored too much in blue and black.