Wirewood Symbiote
The genius of this thing is that it turns Elves from a tribe of static bodies into a recursion engine. Bouncing one of your own Elves looks like a cost, but where the deck cares about enters-the-battlefield triggers it becomes the payoff: every Wirewood Herald, Wood Elves, or Elvish Visionary you return is a trigger you get to fire again next turn. The untap clause is the other half of the loop, refreshing a tapped-out mana Elf so the board never actually slows down. Pair it with an Elf that produces more mana than it costs to recast, and the loop generates card advantage and ramp at the same time. It is also a quiet defensive trick, since returning an Elf about to die to removal or combat saves the creature and resets its trigger, all at instant speed. The once-per-turn restriction holds the engine short of a true infinite on its own; it forces you to assemble the pieces rather than handing over a free combo. That single constraint is why it has aged into a fixture of dedicated Elf strategies rather than a banned curiosity: a one-mana 1/1 that does almost nothing in a vacuum and quietly becomes the most important card on the board the moment there are Elves with triggers worth replaying.
