Xel'lotath

The Xelo'lotath archetype revolves around using reducing the Level/Rank of your opponent's monsters and reducing their ATK by 300, and the Level 5 or higher monsters having effects that take advantage of that reduction. Ideally, both the Spell and Trap effects both take advantage of this level reduction, with the Spells could also reduce it further, and the trap effects also could manipulate the cards in your opponent's hand or Graveyard as well.

Their boss monster is Xel'lotath, the Deity of Insanity.