Producing mana, attacking, and activating certain abilities require tapping a card, turning it sideways to indicate it has been used
They also reflect how returning to this concept sparingly, and not in every set, can mantain the novelty
Here's Kyle's Over/Under predictions for all 85 mono-color base set legends, from Thor to Squirrel Girl
The archetypes which want those kinds of cards are red-white, green-white, black-red, and (to some degree) green red
Cards that care about creatures with power 4 or greater fit naturally here, since green and red already push you in that direction
The counter spells, flicker effects, and untapped mana serve as excellent rattlesnakes that tend to keep this deck in the game all the way to the very end