Syr Konrad, the Grim

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.

Dragons, alongside Goblins, are reds primary creature types. Dragons are reds strongest creatures and most of the expansions have some kind of red dragon in them. As dragons are expensive to cast, dragon tribal decks run multiple cost reduction effects and have ways to cheat the expensive dragons on the battlefield.

Mono blue has multiple ways to clone own or opponents permanents. The gameplay changes effectively, when you get to play your opponents biggest threats, too and clone decks can lead to some very weird and interesting situations.