Sludge

Sludge is a boss in Golden Sun: Dark Dawn. It is a lizard-like monster that haunts the Phantasmal Bog, and is accompanied by a Haunt Skull and a Shield Skull. It has an immunity to Mercury and a weakness to Jupiter. Some of its known techniques include: Crush (target: single character); Tail Slap (target: 3 characters); Call Skull (can only have 3 Skulls at a time); and Healing (heals up to 300 HP).

Defeating it will give you the Crush Tusk. The experience and Coins will be dependent on how many Skulls you have defeated.