Deepcavern Imp

A discard cost in place of a mana payment is the wrinkle that defines this whole transaction. Echo normally taxes you in mana, asking you to pay the printed cost again on your next upkeep; here the second payment is a card from hand instead, which reframes the creature as a black aggro engine that converts cards into tempo. The body comes down and swings immediately thanks to haste, evades blockers in the air, and then forces a choice: feed the graveyard or watch it die. That marriage of haste and a card-based echo means it does its full damage the turn it lands, so the discard is less a tax on the creature and more the price of having already gotten your value. For black decks that want their graveyard stocked, threshold engines, reanimation targets, delirium counters, the upkeep payment stops being a downside and becomes part of the plan: you were going to pitch that card anyway. The Rebel typing is a vestige of an older rummaging-and-recursion subtheme rather than a relevant hook today. What carries the design is the substitution itself, a small proof that echo's mana clause was never the only way to make a sacrifice trigger sting, and that a fast flyer can be honest about its rate by charging you in resources rather than in tempo.