If you have a graveyard full of creatures already, but they have an Archon of Cruelty in theirs, try to set up a Violent Outburst at the end of their turn, and hopefully have a board big enough that you can win in one attack before they get to untap with the Archon.
When you are on the play, try to cast a Grief on turn one to cut them off, discarding an Archon of Cruelty to hand size at their end step.
If they have multiple Archons in their graveyard, you can beat it with two cascade spells – cast the first one, which will return their Archons, and sacrifice creatures to its triggers and use the discard triggers to put more creatures into the graveyard. Then, cast a second cascade spell, which will remove their Archons and return the creatures you sacrificed and discarded to their Archon triggers.
You need to go for a Living End fairly aggressively, as if the game goes long, they’ll be able to beat a resolved Living End by putting multiple Archons into play.
Otawara, Soaring City can fizzle an Indomitable Creativity that is targeting an artifact.
Turn the Earth is annoying to play against as Grief only hits one side of it, and they can play around Force of Negation by timing it properly. The only way to beat it is to try to cycle as much as you can and to cascade at a time that is awkward for them – either they can’t cast it and flash it back, or in response to them flashing it back.