Demonspine Whip

An equipment that converts mana directly into damage, repeatedly, with no ceiling but your mana pool. The structure is what sets it apart from the usual +X/+0 pump: the bonus is a repeatable activated ability on a permanent, not a one-shot spell, so a single attacker can soak as much mana as you can produce across a turn, and the equipment survives to do it again next combat. Equip is almost an afterthought; the to move it between creatures matters less than the fact that the firepower is permanent and reusable. Because the +X/+0 only adds power, this is a finisher's tool rather than a defensive one: it turns an unblocked creature, a trampler, or anything with menace into a clock that scales with your land count, and it pairs naturally with creatures that deal combat damage in ways the defender cannot afford. The toughness staying flat is the honest part of the design: it makes the whip useless on the back foot and pointless on a creature that is going to be blocked and killed anyway, so the reward is gated behind getting damage through in the first place. A red-black expression of "all your mana, into the face," built around the player who has more lands than spells worth casting and an attacker that just needs to hit a little harder.