Excalibur, Sword of Eden

Mana Cost: {12}
Total Cost: 12
Type: Legendary Artifact — Equipment
Description: This spell costs {X} less to cast, where X is the total mana value of historic permanents you control. (Artifacts, legendaries, and Sagas are historic.)
Equipped creature gets +10/+0 and has vigilance.
Equip legendary creature {2}