Without an immediate answer, it has a very high ratio of games that allow it to roll downhill before an opponent can stabilize
Also, tapping a seat to use it's ability can be done at any time an instant could be played
They can even represent completely abstract concepts, like Exploration does
You may have one companion in the Commander variant
And while I dont think itll see much play at all in any 60-card Constructed format, never say never
However, its in Arthurs ability that he truly shines: when played, he can give a chosen character Challenger +2 and Resist +2 (that means they get +2 Strength while Challenging and a reduction of 2 damage thats being dealt to them), plus they can also challenge Ready, not Exerted, characters on the same turn too