You can also probably get away with just running one copy in the deck if you have a card you use to add a little utility or support to your strategy, or one that you use as your silver bullet against certain strategies that are more common in the metagame
Gengar H9 has a powerful attack that either burns or confuses the enemy Pokmon depending on the coin toss, but more importantly, it has the Pok-Power: Manipulate, which allows the player to place a basic Pokmon from the discard pile onto their bench and flip three coins to determine the amount of energy cards the player can attach to said Pokmon from the discard pile
Hedron Fields of Agadeem I like the tension that Hedron Fields of Agadeem provides since the big creatures cant enter combat, but hey, if chaos ensues you get a free 7/7 with annihilator 1
Most Collector Boosters guarantee at least 3-5 rares or mythic rares, depending on the set
Ulalek also has a ridiculous ability in terms of complexity and power level
7 Eldrazi Conscription Akin to creatures out of Lovecraftian horror, The Eldrazi are cosmic horror creatures from the Blind Eternities, first appearing in the Rise of the Eldrazi set in 2010