Demonmail Hauberk

The equip cost is the entire personality. Most Equipment charges mana to move; this one charges a creature, which inverts the usual relationship between a sword and the hand that holds it. You are not paying to suit up a threat so much as feeding the smaller body to grow the bigger one, and the +4/+2 it grants is sized to make that trade pay off in a single swing. That requirement is also the brake: the bonus is large for four mana to install, but every attachment after the first costs another body, so a board that empties out cannot keep relocating the buff. The synergy that matters is not "creatures with high toughness," it is fodder you wanted to sacrifice anyway. Tokens, dying value creatures, anything with a death trigger, and recursive bodies all turn the equip cost from a tax into a second payoff, which is why this reads less like equipment and more like a sacrifice outlet that happens to leave a 4/2 buff behind. The hauberk sits in a small family of effects that bury their cost inside an act of attrition rather than a mana payment, and its appeal rises and falls with how cheaply a deck can manufacture creatures to throw under it.