They transform into a wheelchair.
I don't mean so much that I don't understand them from a pure mechanical standpoint, as I don't understand them from a character design standpoint. The Joker traditionally isn't paraplegic, and in fact does not appear to be so in any of the shots where he's standing. The arms themselves don't have a strong "Joker" aesthetic to them; about the best you could say is they very, very vaguely etch out the sort of "Harlequin Crown" ornamentation, and that's a heck of a stretch.
Pretty much the only connection I can think of is...
Joker in a wheelchair is pretty ironic considering what he did to Barbara Gordon in the main canon
... this, which is some weak sauce, honestly. If it's a new element he's adding to the design that's his prerogative as an artist, but it really should be something that has a clear visual link to the core elements of his design, even if it's in a purely superficial way.
Like, if you did this for The Ventriloquist and the way the mechanical arms moved had a very "puppeteer" aesthetic to them, I could see that.