Basic lands, Foreign, or silver/gold bordered cards
Similarly, if another effect allows you to cast a creature spell from your graveyard, you may use that permission and later use The Tomb of Aclazotz's ability to cast another creature spell
Players hate to give you opportunities for card draw if they can help it the hatred aimed at stuff like Rhystic Study proves that , and pillowforting up with it, Ghostly Prison and Norn's Annex will at least buy you a few more turns or severely disadvantage opponents who try to get through
Teyo, Geometric Tactician Three mana for an on-curve three loyalty
The Rewards There'd be little reason to track down these wily characters without incentive
A lot of commanders that have extremely powerful effects but are very costly like Narset, Enlightened Master and Ramos, Dragon Engine go here