Blightwing Bandit

The condition is the whole design: not "when you cast a spell on an opponent's turn," but your first spell during each opponent's turn, which means the theft engine rewards a player who holds up interaction rather than dumping everything on their own turn. Each opponent contributes one exiled card per turn cycle, and the any-color-mana clause strips out the usual friction of casting off the top of someone else's library, so the card you steal from the blue player is castable even in a mono-black shell. That instant-speed window is the load-bearing part. A flash counterspell, a removal spell, an end-step draw: any of these arms the trigger, so the card asks you to play a reactive game you were probably going to play anyway and taps the reward off it. The 2/2 body with flying and deathtouch is deliberately modest; it wants to connect for chip damage or trade up in combat, not carry the game. What it actually does is convert your normal turn-to-turn interaction into a slow, multi-source card-advantage engine, one top-of-library card at a time, with the theft scaling directly to how many opponents you face. It is a Faerie Rogue built for the political long game, where the payoff accrues to the player who was going to hold up mana regardless.