It might not be the best green commander, but its one of the most interesting
When Dreadhorde Arcanist attacks, the player may cast an instant or sorcery card from their graveyard for free if its mana value is equal to or less than Dreadhorde Arcanist's power
Whenever one of your dragons is targeted by a spell or ability, you get to blow up a nonland permanent your opponent controls
Then you can spend two mana when she dies to shoot each foe equal to her power, so she's a bit of a win-con, and that ability is Rakdos so she's got that color identity instead of Black
Emeritus of Truce The White Emeritus is the only one that can't re-prepare itself and, when revealed, was subjected to hearty guffaws about how WotC always gives white the worst toys
At its best, though, playing a couple of these in a row will allow you to become essentially unbeatable very quickly