Black Market Connections
Black card-advantage engines have always billed you in life on someone else's schedule. Phyrexian Arena draws you a card and drains a point every upkeep whether you want it or not; Dark Confidant chains the loss to your own curve. This one puts the meter in your hands and lets you set the reading each turn. During your first main phase you pick as many of the three lines as you can stomach: a Treasure for one point, a card for two, a 3/2 changeling for three, up to a full six-life bite if you want the whole spread. That per-turn choice is the engine. A fixed "draw a card, lose 2 life" enchantment would be a competent Arena variant and stop there; assembling the payment on the fly, sized to how much life you can spare and what your board needs, converts a static drain into a dial you reset every untap. The Hire a Mercenary mode is the quiet standout: a 3/2 with changeling is a warm body in any tribal shell, but it also feeds a sacrifice outlet, blocks when you are bleeding out, and counts as whatever tribe you happen to need it to be. What the card keeps asking is how deeply to reach into your life total on a given turn, and it lets you answer differently every time.
