Remember how Kid lost an arm during the timeskip?
Now we know that he entered Totland along with Urouge, Apoo, and Capone to attack Big Mom and failed.
Now from not too long ago when we saw the roulette that Jimbe and Zepo spun if you look carefully you can see life and limbs that could be taken.
I think Kid had to spend the roulette to what ever he had done to Big Mom and he spun the left arm and Big Mom cut off his left arm for messing with her. And that his how he lost the left arm and the reason he agreed with Killer on forming an alliance to take down Yonkos because he knows he can’t do it himself. Cause if he didn’t he is such a hot head he would just charge in like Luffy. Anyways that is all to the theory.
Thanks for reading, tell me what do you think?
*Theory by Onepiecefan9867