Keeper

"Keeper", known as "Protector" in the OCG, is the trio of 2 Xyz Monsters and 1 Synchro monsters Tiras, Keeper of Genesis, Adreus, Keeper of Armageddon, and Armades, Keeper of Illusions. Tiras and Armades are LIGHT monsters, but Armades is a Fiend like Adreus.

Tiras, Keeper of Genesis
Tiras cannot be destoryed by card effects, and It can also destroy a card by it's effect after it battles. Buts Tiras only gets these effects while it has Xyz materials. So using cards that adds more materials is a must to keep destroying an opponent's cards and keep it from being destroyed by card effects since Tiras loses a Xyz Material at the players End Phase.

Adreus, Keeper of Armageddon
Adreus can destroy face up cards by removing a Xyz material. Adding more materials to Adreus isn't necessary to be reliable but recommended since Adreus doesn't require the player to remove a Xyz material at the end phase like Tiras.

Armades, Keeper of Illusions
Armades stops the opponent from activating effects until the end of the damage step if it attacks or is attacked. Armades effect makes it useful against Spells and Traps, but it also bypasses the effects of Monsters that require the player to attack or be attacked by the opponent to get their effects. (e.g. Special summons if attacked, Flip Effects, Destroyed by battle effects, etc)