Purphoros's Intervention

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.