The Adversary was the main boss (excluding the Avellian Stronghold) of the Christmas Event 2021. Like the rest of the Avellian fleet, it shares some design traits and armament with them, however the Adversary has a unique vertical design, similar to the Halkaryak. It is also the only Avellian ship (along with its playable counterpart, the Khapri) to be a shield-breaker instead of a hull-shredder.
The Adversary spawned roughly two hours into a round, with no player requirement. When spawned, it was announced at the top of the screen like other bosses. Upon being attacked, the Adversary called all other alien ships to its location. During battle, it tended to hover in place, being able to shoot its enemy from all angles using its superior line-of-sight.
- Although the Adversary has forward-facing weaponry, its turrets can rotate to fire behind and to the sides of it as well. Because of this, the ship has no effective blindspot, so attempting to abuse this strategy proves fatal.
- Gather a fleet of hull tanks in order to shrug off the blasts of the Adversary, however take caution to not be destroyed by the hull-shredding armament of the Adversary's fleet: bring some strong AA ships such as the Tempest to pick off the smaller ships.
- The most popular strategy for killing the Adversary was simply to draw it to a high-level Starbase with a fast ship and draw the fleet's fire while the base destroyed them.
- Drops 80 Snowflakes, 6 Plasma Batteries and 135 Alien Parts.
- Considered to be the easiest event boss due to its measly health and damage when compared to other event bosses such as the Harvest King or Hellkeeper.
- Briefly used the model of the Mantid before it was changed to the Khapri because "Mantid doesn't really look like a boss".
- It can be assumed Adversary's loadout was that of the Mantid's during this period.