Community-reported
Based on player guides and/or gameplay footage, not confirmed directly from the game or the developer yet.
Goblin Shark
A reported Island 5 boss, summoned with a Scientific Boss Lure.
How to Find It
Summoned with a Scientific Boss Lure, per Destructoid.
Existence is corroborated by two sources (Game8's boss list, Destructoid's), but the island placement and bait are single-sourced (Destructoid only; Game8 marks this boss's details as "TBD").