Nurgle's Rot
It still feels lesser among the mythics in this particular set, but it gets some major points for being a card that makes you think about how to make it work effectively
Eye of Singularity If your table is drowning in Treasures, Clues, Foods, and copy effects, Eye of Singularity can feel like a rude reset button
Actually, fellow Dominaria United card Resolute Reinforcements is also relatively popular as a Foundations reprint, but I decided to just put Tolarian Terror as the sole "actually still Standard legal before being immediately reprinted" on this list
Not only does the end step trigger potentially draw you a card each turn, Curiosity and its many variants also work for oodles of card advantage
(Do this before you draw.) Illustrated by Yigit Koroglu Standard Not Legal Alchemy Not Legal Pioneer Legal Historic Legal Modern Legal Brawl Legal Legacy Legal Comp