Hostile Investigator

Discard as a mechanic has always fought against its own tempo: you strip a card from the opponent's hand, but you fall behind on your own count in the process. This design closes that gap by wiring the two halves together. The enters-the-battlefield discard is the trigger, and the second ability catches it, turning every discard into a Clue. The card that leaves their hand is replaced, on a delay, by a card into yours. The once-each-turn clause is the restriction doing the balancing: it stops repeatable discard effects or symmetrical wheels from spinning out an arm's length of Clues in a single turn, keeping the engine to a measured pace rather than a runaway one. What makes the second trigger sharper than it reads is that it watches for any player's discard, so hand-attack elsewhere in the deck, cleanup-step overflow, or an opponent's own discard costs all feed it. The 4/3 body is priced to pressure rather than block, which matches the job: this is a black midrange threat that wants to trade attrition while quietly banking card advantage in artifact form. The Detective typing and the Clue payoff put it in the same family as the investigate archetype, but the discard clause is what gives it a distinct axis: it does not just gather evidence, it manufactures the crime scene first.