All battle-ready Sentinels fight a common enemy at the same time. Cooperation is needed to fend off the waves of enemies. Bosses come in three types: Virons, Phantoms, and Cyberions

Each Sentinel must identify its role in the boss battle: buff up its damage or resistance, or attack the boss. Choosing wisely will ensure a Sentinel is maximally rewarded.

Any Sentinel that contributes to the defeat of a boss will earn runes for their valor. Runes are important to revitalize a broken Sentinel and for purchasing upgrades and add-ons.

Each new boss will pose new threats. Sentinels may need to coordinate activities to ensure they can defeat each new boss.