less to cast, where X is the total mana value of historic permanents you control. (Artifacts, legendaries, and Sagas are historic.)
Excalibur, Sword of Eden gives a legendary attacker a huge power increase while rewarding a battlefield of historic permanents. Its twelve-mana cost is reduced by the total mana value of artifacts, legendary permanents, and Sagas you control. Once attached, it grants +10/+0 and vigilance, letting the equipped creature threaten substantial damage while remaining available to block.
Legendary creature decks and artifact-heavy Equipment decks can reduce the casting cost naturally. A permanent that is both an artifact and legendary still contributes its mana value once rather than being counted twice. Tokens with no mana cost usually contribute nothing to the reduction, although a token copying a permanent can have that permanent's mana cost and therefore a meaningful mana value.
Sigarda's Aid can attach the Sword when it enters, while Stoneforge Mystic can find it and provide another way to put it onto the battlefield. Its own equip ability specifically equips a legendary creature, so ordinary creatures are not legal targets for that activation. Other attachment effects can operate under their own instructions, which creates flexibility in a dedicated Equipment list.
The Sword grants neither trample nor another evasion ability. A small blocker can still stop a large attacker from dealing damage to a player, so a naturally evasive commander is a strong carrier. Plan for the actual attack as well as the discounted cast: the best setup combines a cheap deployment, a legal attachment route, and a creature capable of connecting.
