Caesar, Legion's Emperor
Sacrifice on attack is the whole engine, and it is built to feed itself. Throwing a creature under the wheels before combat resolves buys a menu of two, and the first mode refunds the cost twice over: two Soldiers arriving tapped and attacking, ready to become fodder next turn. That loop is the spine of the design, because the third mode scales off tokens, a mono-red-style reach effect that grows every time you manufacture more bodies to feed it. The middle mode (a card at the price of a life) is the least flashy and the quietly load-bearing one, keeping the aristocrats machine from stalling when the board thins out. What makes the trigger unusually demanding is its sequencing: it fires on the declaration of attackers, so you commit the sacrifice before you know how combat shakes out, and the tokens it spits back are locked into the current attack rather than banked for defense. Every combat step becomes a small optimization problem about how much board to convert now against how much to save for the burn later. A four-mana three-color 4/4 that wants a wide, expendable board around it is asking for a specific shell: token-makers, cheap chaff, and a reason to keep swinging into a losing race. When the shell is there, the ceiling is a chain of Soldiers converting straight into face damage; when it is not, this is a 4/4 that would rather not attack alone.
