Tax Collector

The choice between the two modes is where this card earns its keep, because they answer different threats on different clocks. Tax is a stax effect on a body: a one-turn tariff that punishes an opponent trying to unload their hand, and its value scales with how many spells they want to cast before your next turn resolves it away. Arrest is the reactive line, a detain that neutralizes an attacker or, more usefully, shuts off an activated-ability engine for a turn: a mana creature, a planeswalker-adjacent threat, a combo piece that needs to tap. Detain as a keyword has always been a soft, temporary answer rather than a permanent one, which is why stapling it to an enters trigger works: the creature stays on the board as a 2/2 body after the detain wears off, so you are never spending a whole card just to buy time. What makes the design cohere is that both modes are prophylactic and both expire on the same clock, so the card asks you to read which pressure the opponent is applying right now: are they trying to cast their way ahead, or attack and activate their way ahead? The enters-the-battlefield timing means the choice is locked when the creature arrives, with no way to hold the mode open, which keeps a flexible card from also being a reactive trick.