Seam, the enigmatic shopkeeper, runs a mysterious shop in Castle Town (Chapter 1) and later in Castle Town (Chapter 2). He sells unique items and provides cryptic lore. More importantly, Seam is the key to unlocking the game's secret bosses.
Chapter 1: Jevil
To fight Jevil, you must first collect three key pieces: the Bake Sale Key, the Mansion Key, and the Forest Key. These are found in various hidden locations throughout Chapter 1. Once you have all three, return to Seam, who will combine them into the Jevil's Key. Use this key on the locked cell in the Card Castle basement to challenge Jevil. Be warned, Jevil is an incredibly difficult optional boss, requiring precise dodging and strategic use of ACTs and items.
Chapter 2: Spamton NEO
To fight Spamton NEO, you need to acquire the PuppetScarf and the Dealmaker. The PuppetScarf is obtained by completing a series of tasks related to Spamton in Chapter 2, often involving finding him in various locations and purchasing items. The Dealmaker is found in a hidden area after solving a complex puzzle involving the 'Acid Tunnel of Love'. Once you have both, return to Spamton's shop in the garbage dump and interact with the 'Empty Disk' to initiate the fight. Spamton NEO is another formidable challenge, testing your reflexes and understanding of the game's combat mechanics.