Soul Fysh

Soul Fysh is one of the Act 1b bosses encountered in the Underdocks and is a new boss introduced in Slay the Spire 2. This aquatic creature uses unique mechanics that set it apart from the returning bosses, testing players with a combination of damage, debuffs, and mechanical complexity that can catch unprepared decks off guard.

The Ironclad should approach Soul Fysh with a balanced deck that can both deal consistent damage and maintain Block. Bash applies Vulnerable for amplified damage, while Shrug It Off and Flame Barrier provide reliable defense. The Silent's Poison from Deadly Poison and Noxious Fumes is effective since Poison ticks between turns regardless of the boss's defensive patterns. Footwork helps the Silent maintain Block through the boss's damage phases. The Defect's Lightning orbs provide steady damage, and Frost orbs generate passive Block to handle incoming attacks.

The Necrobinder's Osty acts as a damage buffer against Soul Fysh, and Doom stacks provide an alternative win condition that bypasses the boss's defensive mechanics. The Regent can use the fight's pace to balance Star generation with combat effectiveness. Soul Fysh is often compared to Lagavulin Matriarch as the alternative Act 1b boss, with each boss favoring slightly different deck archetypes. When choosing the Underdocks path, consider which boss matchup is more favorable for your current deck and character. The Lava Rock Ancient blessing makes both Underdocks bosses more rewarding with double relic drops.