Ostium

About this board game

Ostium is a turn-based deck-building card game for 1–3 players, with games typically taking around 40 minutes. In a conflict between eternal enemies, planar gates open across another world and unleash powerful creatures into a fight for dominance.

Each player uses their gates to summon creatures and attack opponents’ gates. Every creature has its own abilities, which can become stronger when supported by other members of its clan. Creatures can also fuse with energy channeled directly from a planar gate, dealing crushing damage to enemy gates or creatures.

Each turn is divided into two phases. During the first, players bring additional forces to the battlefield and use the special abilities of their summoned creatures. The second is the combat phase, when extra powers, channeled energy, and clan synergies are unleashed against opposing forces.

• Summon creatures to the battlefield or discard pile.
• Arrange creatures in attack or defense rows to shape their abilities and power.
• Use card order, creature abilities, clan support, and gate energy to plan each assault.

Card order is a crucial part of play: neither the deck nor the discard pile is shuffled, so the sequence in which cards are placed, drawn, and played can determine the outcome. The position of creatures on the battlefield also has a major effect on their abilities and strength.

Originally designed as a duel game, Ostium also includes rules for solo play and three-player matches. Its combination of tactical positioning, hand and deck management, and creature synergy creates a focused battle for control of the planar gates.