Quick Restoration also synergizes with Arthur's stats well since he is unable to be KO'd by 1 ATK or lower if he is at full HP. This makes him very likely to get off a big heal from it to further make himself hard to KO.
We Are Waruda is a great card to bring since it allows Arthur to move his shops after someone has landed on it in order to prevent it from being destroyed by a trap
Completion Reward synergizes with Arthur's shops since it can be stepped on multiple times. However, he finds this card to not be too helpful since his star gen is already much better than most characters if he has shops up.
Level 1 traps like Bad Pudding and Sealed Memories are the best way of preventing Arthur from snowballing the game before he profits too much from getting his hyper early. Bad Pudding is the best level 1 trap to bring since if he lands on it, he will lose a card that could be useful to him.
Scrambled Eve and Gift Exchange can remove cards that Arthur needs, including his hyper if he wasn't able to draw it before someone else got to norma 3.
While this card is almost always suboptimal to bring, Exchange will most likely harm Arthur significantly since he often has a massive star lead.
While Brutal Prank, Flamethrower, and Present Thief seem like they would do well against Arthur, the threat of him getting his hyper early means that the level 1 traps should always be taken over these.
Another card that seemingly counters Arthur, Star-Blasting Light is a terrible card to bring because by the time it can be played against him, he has most likely profited greatly off of his hyper, and the 50 star cost will most likely cause the user to lose the game. It must be decked with both President's Privilege and Play of the Gods which takes up a further 4 deck spots, and those combos will still most likely fail since there will most likely be only one copy of Star-Blasting Light in the deck, which makes even getting it very unlikely.