Teamwork makes the dream work! That’s the idea behind Yugioh! Union Monsters. Teamwork! But, what is a Union Monster? These monsters work together to achieve a variety of goals, whether working in tandem with other Union Monsters, or with your other monsters. Let’s take a closer look!

Union Ability
Union is a monster Ability that allows the player to equip that Union Monster from the Field to another monster as if it were an Equip Spell. All Union Monsters share the same effect: “Once per turn, you can either: Target 1 face-up monster you control; equip this card to that target, OR: Unequip this card and Special Summon it in face-up Attack Position.” Many Union Monsters can be equipped to any other monster, but there are some that only work together with each other, like Kiryu and Dark Blade or Burning Beast and Freezing Beast.
Union Effects
In addition to their shared equipping effect, Union Monsters also have effects, or grant effects while equipped to another monster. Union Monsters all protect the monsters they are equipped to. If your monster equipped with a Union Monster would be destroyed by battle or your opponent’s card effect, the equipped Union Monster is destroyed instead! And that’s not all! Unions also have their own effects. Zombie Tiger grants Decayed Commander an ATK/DEF boost, and, when your Decayed Commander deals damage to your opponent, your opponent must discard one random card. That effect stacks with Commander’s own effect, too. So, if your Commander equipped with Tiger attacks your opponent directly, they have to discard 2 cards!

Union Archetypes
Now, Unions are a lot like Gemini Monsters in terms of popularity and playability. The problem with Unions is that, like Geminis, is that they are too slow and cumbersome to actually use effectively. This mechanic, while interesting, just never took off or became viable. And as of today, there are only 40 Union Monsters in the game. While there are no Union-exclusive archetypes, there are some that make use of these unique monsters. Valkyrie, Machina, Heavy Mech, Vylon, and the LIGHT Machine Tank/Cannon cards all have some Union Monsters in their ranks.