Phyrexian Marauder

A colorless mana sink that pays for itself only once, then taxes you forever after. The X spent at casting buys raw counters, but the build is rigged so those same counters become a permanent attack tax: every point of power you paid for has to be paid for again, in full, each combat you want to swing. That is the design discipline holding the rate in check, and it is a deliberately punishing one. A creature that costs X to deploy and then asks for another sum equal to its power just to enter combat is a body that grows expensive to use as it grows large, which inverts the usual logic where bigger creatures earn their keep by attacking freely. The "can't block" clause closes the obvious escape hatch of parking it on defense and letting the counters sit. What you are left with is a vanilla-looking artifact whose every line of text is a leash: a Phyrexian Construct that the colorless cost makes castable in any deck, but whose entire structure is built to make sure raw stats alone never translate into free pressure. It reads like an early experiment in pricing a creature's offense separately from its existence, a question Magic's design would keep returning to in cleaner forms.