Ok, i'm a bad diesiraeposter, but basically it started when Disney made a Star vs. promo where "Dies Irae" was background soundtrack.
Basic points are: Star=Venus=Morning Star=Lucifer, Marco=Mars. This theory somehow predicts Starco as canon but simultaneously it's kinda bad? Also Star is a devil according to this.
And also some proofs include Star being a rebel (like Lucifer) and her new Mewberty form (literally a star, has demonic voice and symbols in eyes + new wand design) and Marco being attracted to red (color of Mars), his wand (Mars's spear) and Oscar's keytar landind on his doorstep in Starcrushed ("do you think it will land on Mars?")
Pic related was made long time ago, i hadn't even known about /sveg/ but i guess it were pre-Bon Bon times.