Oh shit, it turns out all Bowsette was missing was a little Judgement!

>mega fury bowser
Wasn't the name "god slayer bowser"?

RIGperu said:

>mega fury bowser
Wasn't the name "god slayer bowser"?

It's apparently neither. Matt Mcmuscles made up the name, and it spread like wildfire. The idiots at Screen Rant even claimed the names to be official in an article, citing Matt's tweet.

The Japanese used to refer to Bowser's new form is just "Giant Bowser"

Created a wiki for it. Feel free to modify when the official name is going to be revealed.