Cryptic Gateway

An entire creature-types-matter block built its payoff structure around enablers like this, and few of them feed a board into itself quite so literally. Tap two creatures, drop a creature from hand that shares a type with each, and the cheat costs nothing but the tap: no mana, no sacrifice, just a wide enough board willing to commit. The chain potential is the whole appeal, because each creature it deploys can be tapped to deploy the next, turning a stalled-out army into an engine that empties your hand. Untapped Goblins or Elves can fast-track a body far larger than the activation should buy, and the type-matching requirement on both ends is the only governor on the loop: every entering card must share a type with each creature tapped, so the card lives in single-tribe decks dense enough to make the math reliable, or in changeling shells where every creature counts as every type at once. The deck has to declare a creature-type identity before the gateway does anything at all, and the reward for that commitment is hand-emptying acceleration that spends no mana at all. It sits a step away from the lords and anthems most type-themed decks run on; rather than buffing a team, it converts an existing one into a cheating-into-play machine, a stranger and more open-ended job than pumping the board.