MK-X

The MK-X (MarK-X) series of bosses based on the Square. This is the first X-K-X boss, surpassing even EK-X and TK-X. Originally, it was named MK1 and was added on October 7, 2018. MK-2 and MK-3 tiers were added the same day. MK-4 was added later on the same day, four hours later, and the tier system was renamed to MK-X one hour later. MK-5 was added on July 15, 2018, and was heavily nerfed the same day. Originally, it had six minions of both types, but now it has only three minions of both types.

MK-X series is mainly based on swarm drones and all have a square yellow base. MK-1 is even weaker than EK-1, but all higher tiers are more based on swarm drones. Minions are also a pretty important part of the MK-X boss. MK-5 is based on bullets, swarm drones, and minions. MK-2, MK-3, and MK-4 are more based on drones/swarm drones. MK-4 is mostly based on swarm drones, as they are very strong. Also, MK-3 has a Hybrid auto-turret, which is obtained only by a few other bosses like C.L.O.C.K. or Destroyer.

MK-X cannot currently spawn in the game under any circumstances and is on the TESTBED bosses branch. The two highest tiers are blatantly OP, and MK-5 can cause some lag to the server because of its bullets, size, and minions.