Rise of the Floodborn added a unique card strategy with bouncing Merlins different shapeshifted forms back from your hand (especially Merlin: Goat), gaining their powerful played abilities over and over again
Tasigur, the Golden Fang Tasigur, the Golden Fangs size as a 4/5 for potentially 1 mana is already good, but the fact that it has built-in card advantage is what seals the deal
The World Tree and Maskwood Nexus combo together to pull all your creatures out of your deck
Taii Wakeen, Perfect Shot The draw ability on Taii Wakeen, Perfect Shot is strong, especially with spells like Earthquake that hit multiple creatures, but were here for the second ability
At time of writing, there are only two known commons that reward this unnamed mechanic: Arena Trickster, which turns from an unexciting Hill Giant into a Rampaging Baloth (and can continue to grow), and Naiad of Hidden Coves, which allows you to play two Vexing Gulls on turn four