Selvala, Heart of the Wilds

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.

Decks with heavy focus on "at the beginning of combat" triggering commanders synergize well with extra combats. Extra combats decks' main strategy is often multiple extra combats or even infinite amounts with a combo!

Combo decks are control heavy decks, running a heavy amount of card draw or tutors. If the decks get to assemble the combo pieces the game often ends in an infinite combo.

As green has the best mana ramp options in the format, and the biggest creatures, too, it is only natural that big creatures / stompers decks are popular in mono green. Stomper decks have lots of ramp in them, and aim to cast big creatures to wreak havoc to the opponents.