"Mask" (Japanese: 仮面Kamen) is a series of cards relating to masks, mostly used by Umbra and Lumis in the second series anime. The cards focus on limiting the actions the opponent can perform.
The main strategy for a Mask Deck is to prevent your opponent's monsters from attacking while damaging their Life Points at the same time. Also, "The Masked Beast", a Ritual Monster boasts a powerful 3200 ATK and "Masked Beast Des Gardius" has 3300 ATK and the ability to activate the mask of remnants upon destruction, which can take control of an opponent's monster.
One good combo is to use "Mask of the Accursed" to stop an opponent's monster and take 500 Life Points from them each turn, and use "Mask of Dispel" to damage them even further and "Mask of Restrict" to stop them from Tributing the monster. Equip Spell Cards are a good choice for this Deck because you can power up your non-Tribute Monsters while "Mask of Restrict" is in play. "Mask of Brutality", however, is often tossed out for other Equip Cards due to its cost, though if you had 2 copies of "Life Absorbing Machine" out on the field, you would gain the life points that you just paid. Ritual Monsters and/or Fusion Monsters are also a good choice for this Deck to take advantage of "Mask of Restrict". "Lava Golem" is a good choice as fits with the Burn theme and can be equipped with "Mask of the Accursed" and kept on the field with "Mask of Restrict".
Another good card for the deck is Dark Resonator; due to the abundance of level 4 monsters, you can easily summon Dark Highlander, which stops your opponent from Synchro Summoning and can easily destroy almost any Xyz in battle.