The TAG System in a core feature in Master X Master that allows players to pick two Masters before a match, and swap them in and out mid-battle to use their specific skills, and build powerful attack and defense combos - or even avoid death.
Players can pick contrasting Masters to build a powerful and well-rounded duo, or specialize to combo similar abilities, and focus their effectiveness. There are many different combinations and so many strategies to pick from. Masters don't share a health bar, but if one of them dies both will be defeated. Swapping to other Master can help prevent the enemy from landing a final killing blow, but CC and other quick bursts make the decision of when to swap a critically important one. Additionally, many buffs and effects will stick around between masters.