Vivien's Arkbow

Set a single X and it pays for everything at once: the mana you sink in, how deep you dig, and the largest creature you are allowed to drop out of the pile. That triple duty governs the whole activation. Pump six mana and you can hunt for a bomb; spend one and you are peeking a single card down for a mana dork. Because the cost tracks the size of what you cheat in, this is not a discount so much as a redirection: you spend nearly the creature's worth of mana to skip its casting cost and slide it onto the battlefield without ever putting a spell on the stack. The creature never gets cast, so it dodges counterspells that answer spells, though the activation itself still uses the stack and can be met by a Stifle. The discard tacked onto every activation pushes it away from clean fair midrange and toward decks that want cards in the graveyard anyway, where pitching one per turn stops being a tax and starts being fuel. Unlike a fixed cheat-into-play button like Elvish Piper, the X is a dial rather than a set threshold: you reset the ambition every turn based on what your mana and your library can support. And because everything you looked at but did not take goes to the bottom in random order, you commit to the depth before you know whether anything down there is worth finding.