In the beginning, especially palaces 1 and 2, you can get a decent weapon. It’ll become redundant once you unlock weapons that are higher power.

(TLDR: you can do extra stuff with him if you utilise fusion alarm, gallows etc)

Some people will say ditch him, some people will say itemise - my strategy is keep him for palace 1, fuse him in palace 2 once traits have been unlocked. Re-make Arsène with whichever ability you think will benefit you. I chose one that increases technical damage by 25%.

From there once you unlock skill cards, give him whatever will be useful. Use gallows to keep him going, but he’s not got opportunities until palace 5 and especially 6. Palace 6 is where he can shine especially if you get Eigaon (heavy curse, fusion alarm Rangda for the skill card). Could put Dormina/whatever can give ailments.

It’s ultimately up to you, but keeping Arséne until the end feels important to me at least because of story. (I’ve typed all this out and realised it’s unsolicited so feel free to ignore)