Overboss is a simulation strategy game where players assume the role of a dungeon-building "Boss." The core gameplay loop involves drafting terrain tiles and monster tokens from a shared market each turn. Players then strategically place these tiles onto their personal map, aiming to create advantageous adjacencies and collect specific terrain types for scoring. Monster tokens are placed on terrain tiles, granting bonus points for matching icons and creating "bands" of monsters for larger scoring opportunities. Portals allow for monster movement, and Crystals serve to multiply a player's accumulated power. The objective is to achieve the highest score and be crowned the ultimate OVERBOSS.