My money's been on him doing all of this just to push the Butterflys' to their limits since Season 2.
When he told Toffee "I'm not on anyone's side" he meant it. Not because he was in any way neutral or bound to serve the owner of the book or wand, he's really just doing all of this because he wants to and all of the rules he pretends to follow just create plausible deniability. He's done absolutely nothing but what he had to since his "rebirth" (leading Star to Eclipsa to introduce them and then to save her from being frozen again, and getting Eclipsa to save Star and Marco from being lost in the Void) but he can still play it off as "I was trying to warn you about Globgor the whole time" and everyone thinks "yeah that's just fucking Glossaryck."
He set the release of Eclipsa in motion 20+ years ago, and however things play out he's either created the ultimate villain to push his protégé Star beyond her limits again, or he's back with the most talented Queen to ever live ready to start with a new (old) bloodline of Butterflys.
No matter what, he wins.