Nova here.
When Siffrin was becoming massive and huge at the end of act 5 it's my personal headcannon that he was becoming a god.
To become a god you need three things, a domain of influence, a lot of power, and a proper divine mindset.
When Siffrin turned big that was him ascending to a state of divinity specificly into a God of time as his looping has given him power and control over time just through his emotions and willpower alone, sure his own raw power was doing non of the heavy lifting but the power was still under his control regardless.
Then he had accepted that the kings mindset was right and deemed that he had control of time to a degree and that he had a grasp on potentially true eternity
Looping with his family for all of eternity a genuine thing that could be seen as infinite, something that by all accounts is impossible. Something no mortal mind should be able to comprehend, but Siffrin did giving him a divine realization
His realization of that is what starts his metamorphosis his first stage was becoming big firn and in that state he was a nascent god freshly born and created only beginning to understand there power.
There theoretical second form would happen once they looped one final time, mastering his power truly. Having accepted the mindset and the power with there domain already chosen Siffrin would have become a god of time to what degree I know not, and how this would effect him and his mindset I again can only speculate.
GOD SIFFRIN.....OMG... /POS
