It doesn't have to be the same player, planeswalker, or battle that Arthur or any other attacking creatures are attacking
If a good card hits the graveyard, let's borrow it with Reanimate or similar effects
A big part of that comes from Zimone, Mystery Unraveler, who is such a terrifying commander, able to cheat giant creatures onto the board, and facedown, which will always leave your enemies second-guessing
I think Wizards choice to make the exclusive cards legendary creatures was a great idea because it increases the likelihood that theyll see play outside of Game Night
You can cast it as a Force Spike for 2 mana and counter your opponents 2- or 3-mana play, and you can put any amount of mana into it later to counter bigger things