I’m pretty fond of Butler (and not just because he’s a cute ex-Magma). He’s quite fleshed out for a one-shot antagonist (flashbacks! backstory! a girlfriend!), and his character growth in the film is such that you could have completely removed Ash and company and it would have done nothing except make the film better. Granted, I’m contractually obligated to say that about everything, but I think you could literally have erased Ash, May, Brock, and Max from the script and it would have barely affected the plot, because all of the character development happens with Butler.