The Union is the fifth boss from Metal Slug 7.
The battle starts as the 3 units follow you from behind and immediately separate to attack you. They first come combined, then separates to attack, hence the name. To destroy it, the player must first destroy its cores, namely a large, red 'button'. Each unit has its own ways of attacking.
The Head Tank (with the number 01 on the front) has 4 main attacks. The core located behind it fires energy projectiles. The head will open up to fire a guided missile, but this missile can be shot down or dodged. The launcher on its sides launches ballistic missiles that will fall to the ground and explode. There is also a energy mortar on the back platform. A way to destroy this unit is to go to the core and destroy it with Machine Guns, or use a Shotgun or a Powered-Up Shotgun from the front, the latter being much more riskier but faster.
The V.T.O.L. Gunship (number 02) above both units has 4 main attacks. The core is located on the belly of the gunship . It also fires energy projectiles, so take caution when destroying the core. The door on the front will either launch Element Pods or fire a minigun closely similar to the Dragon Nosuke, just more rapidly and moves up and down quickly. When all segments join together, the laser gun on the tail of the gunship will fire. Use a long-ranged weapon for this fight, or go under it and shoot it, more accurate but riskier as the VTOL may crush the player.
The SLAVE Tank (with a number 03) has only 2 main attacks. The core located in front also fires energy projectiles and Multi-cannons will open up on its sides firing bombs in the air similar to the bombs the Hi-Do uses. It is easy to destroy this unit as firing on it will just require the player to stand on the Head Tank's platform. Just be careful when the units join up.
When a unit is destroyed, it will explode and turn blue, but will continue to attack and separate/join up.
When all 3 cores are destroyed, it will keep moving forward and crash, maybe onto a wall, presumably as its cores are non-operational and systems are dead (this unit may be an unmanned vehicle). The player will jump down when The Union rushes forward, and parts will fly everywhere once the mission is completed.
- This boss resembles the fifth boss from the game R-Type.
- This is the only boss in the series to be able to split into different parts during a fight.
- It seems to resemble the chopper boss from Gunforce 2, albeit, being land based and it being a tank than a chopper.
- The Union appears as a Day Specific Mission boss in Metal Slug Attack on Tuesdays-Wednesdays, each part has its own base health, similar to Crablops as its own DSM boss.
- When Union still not separated, it was invincible, player can only damage it when there's unit close enough,making the part get separated. and when get separated, the movement speed is drastically increased.
- Each of the Unit has its own special attack and skills, The Unit #01 can knockback enemies, while the Unit #02 has a chance of getting a critical attack, and the Unit #03 can stun enemies. All of them which can also perform a suicide attack without any skills required.
- This unit appeared in Extra Ops "Agent Sally" of world ranking event
- A version of the third unit is deployed by the Ptolemaic Army in Metal Slug Attack, piloted by Dragunov.