Azorius Arrester

Detain is tempo expressed as a creature-and-a-half: the keyword bolts a creature shut for a single turn, and stapling it to a two-drop body means the effect arrives attached to something that also pressures the board. The trade is in the words "until your next turn." This is not removal; the detained creature comes right back, so the value is purely the swing the turn it triggers. A flier or attacker that can't block while you push two more damage in, a blocker frozen so your other creatures connect, a mana creature or activated-ability engine briefly switched off. That window-buying is the whole reason a 2/1 with no evasion earns a slot in a deck that wants to curve out and tax the opponent's turn. The fragility of the body is the cost of the front-loaded value: a 2/1 trades down to almost anything, but by the time it does, the detain has already happened and the tempo is banked. It belongs to the white-weenie tradition of small soldiers that do one clean thing on the way in, where the enters-the-battlefield trigger matters more than what the creature does for the rest of the game. You pay full price for the body and treat the detain as the reason the card is in the deck at all.