Do you mean the one that I did the worst job on the one that was the hardest? I'll answer both.
Worst Job: Struggle. The struggle with this move isn't even over yet. I've made a couple of variants and they have all made Ame and Inuki cry, laugh and die.
Hardest: Water Pulse is still probably my biggest enemy. It looks good now but it took so bloody long, was irritatingly difficult and as I fixed things, other problems would arise. Yeah so that's probably my least favourite move at the moment.