My first ever guide! Writing this was just as tough as completing the actual mode; I actually had it nearly finished over a week ago, but a browser blunder ended up deleting the whole thing! ARGH! It happened very much the same way as the last boss's final phase, too.
Planet Robobot is definitely one of the tougher Kirby games out there, so I hope this guide will hope those struggling with the mode. Remember: use Stone!