The Eye of Cthulhu from Best Melee Weapon Terraria
Easily the best weapon in Terraria by name and origin; it's a reference to a charactar in Lovecraft's stories. It is the second strongest yo-yo in the game, only giving way to the Terrarian. It deals 115 damage upon attack but only has 4% critical chance. Quick tip, Yoyo Bag will increase damage output.