God-Eternal Oketra

Dredge is triggered ability for a card with dredge ability. It triggers whenever you have a card draw, and it basically allows you to return the dredge card from your graveyard to your hand and mill the amount of cards named instead of drawing a card. Dredge is very strong ability for recursion and milling your self.

The ways to discard are plenty: cycling, rummaging, end steps discard phase, to name a few. Discard decks are built around triggers from discarding, like madness and synergizes well with reanimating.

Aristocrat decks are a combination of sacrifice effects, reanimating and value creation. Wincons revolve around multiple triggers, either from dying, ETB or cast triggers.

Reanimate decks brings back creatures from the graveyard straight to the battlefield. The reanimated creatures are often expensive to cast, like demons, and are complete haymakers compared to the reanimation costs.

Milling in mono blue can be done in two clear ways: self-mill or regular mill. In self-mill, blue usually tries to find some kind of an infinite loop piece and retrieve it from the graveyard or run the Thassa's Oracle or Laboratory Maniac combo. In the regular mill the goal is to mill opponents whole libraries and win by having an opponent draw from an empty library.