Temur Sabertooth

The engine is a single conditional, not a choice between two modes: pay one and a green, and if (and only if) you return another creature you control to your hand, this Cat gains indestructible for the turn. The bounce is the price; the indestructible is the reward for paying it. That coupling is the whole trick. Return a creature whose enters-the-battlefield trigger you want to fire again, recast it, and you have converted four mana into a value loop that runs as many times as your mana holds; the same activation shields the Sabertooth from a board wipe or a bad block in the bargain. The governor is your own hand and floating mana: each loop costs one and a green plus the recast, so the recursion is rate-limited rather than free, and you cannot buy the indestructible protection without giving up a body on the battlefield to do it. What sets it apart is the color it lives in. Reusing creatures-as-triggers is usually blue's job, leaning on bounce spells and flicker; green tends to treat creatures as statlines. This is a green creature that thinks in loops, and a 4/3 that earns its keep in combat before you ever start chaining entries through it. The body attacks into most defenders, and with the ability online it blocks anything once and survives, so the card pays rent whether or not you ever find the enters-the-battlefield engine to build around it.