I was wandering around the site... on the Roar of Time page, it says Kommo-o upgrades the move to its Z-move. Is it possible that Kommo-o can learn this in USUM?
It is probably an error, since the only Pokemon that can learn Roar of Time is Dialga (Discounting Metronome). Clanging Scales is what Kommo-o actually upgrades into its Z-Move.
According to both Bulbapedia's page on Kommo-o and Serebii's page on Kommo-o, Kommo-o cannot learn Roar of Time. It's an error with this site.
Also, the same error pops up on other pages, (I'm assuming that it's all of the pages for Dragon Type moves.) for example, Core Enforcer.