High-level monsters like Doom Shaman and Invader of Darkness require tributes to be normal summoned making them slow and inefficient. So it would be better to send them to the graveyard, where they can be revived practically for free with card effects. Use Featherizer to mill Doom Shaman from your deck, and use your skill Fiend Farewell to mill Invader of Darknessfrom your deck. If in your hand, you can discard them as cost to use your counter trap cards.
Set Featherizer to take your opponent's attack, then mill Doom Shaman from your deck and draw a card when he is destroyed. With this you can thin your deck and effectively stall without losing card advantage.
Preventing your opponent from making plays is one of the strong points of this deck.
By simply having Invader of Darkness face-up on the field, you shut out every quick-play spell your opponent has, making them dead cards in their hand or field. Most devastatingly, is the fact that many meta decks heavily rely on quick-play spells for protection and support.
Use Divine Wrath to negate your opponent's monster effect by discarding a card form your hand. Usually you would want to discard a high-leveled monster so that you can revive them later.
Use Ultimate Providence to negate any card effect by discarding the same type of card from your hand. Best to always have a trap card in your hand when this is set so that you can negate Mirror Wall.
Deck is fun but can easily run out of play options. If you can get Doom out and pull invader etc then you're looking good. Otherwise you're just setting for them to be destroyed :/ I'll stick to 3SD TBD!