Master Eddy is a boss in Mother 3. He is met at the end of the long Sea Floor Dungeon leading to Tanetane Island. He is encountered as the player is heading towards the shore, sucking them in with a whirlpool before attacking. Master Eddy appears as a swirl-shaped being.
Master Eddy, like most bosses, also has an unused back sprite.
Master Eddy can attack twice in one turn, and often generates whirlpools that can hit the entire party (in addition to standard attacks). He is vulnerable to Thunder attacks.
Master Eddy is somewhat unique in that he cannot be defeated like a standard boss: instead of granting experience, the signal for his defeat is when he generates a whirlpool with the last of his strength. This whirlpool will mortally damage the party (it deals around 650 HP of damage to everyone), and all unequipped items get washed away. The party is washed away as well, and they end up on Tanetane Island.
Its battle sound is Battle Sound 17 which falls under Code Numbers 487 for regular attack, 488 for Smaaaash! and 489 for Miss.