The Waterfall move

[Chroma]

We need the HM for Waterfall. Even though we can breed it onto Swampert and Feraligatr, the other physically oriented Water-types like Gyarados and Delta Haxorus really miss out. Aqua Tail is OK as a substitute in the meantime, but its accuracy is questionable.

Also we have the HM for Fly and Surf, then why not Waterfall?