How much do we know about the alternate timelines glimpsed in some Planar Chaos cards?
As far as I can tell, there are only a couple where there’s an actual story behind the Planar Chaos alternate timelines.
The first is from the novel Planar Chaos, where Ice Age adapted Phyrexians invade ‘our’ Dominaria. All we know about them is that they’re from a world where the Ice Age never ended. It’s not clear if it’s because Mairsil accesses Phyrexia like he wanted and Jodah couldn’t stop him, or because Heidar of the Rimewind and his Coldsteel Heart-powered Phyrexians weren’t stopped, or because Phyrexia just invaded sooner (for instance, if Mishra won the Brothers War). This timeline doesn’t actually show up on the cards.
The second is an Alternate Weatherlight Saga where Mirri, instead of Crovax, finishes Selenia and is cursed. This timeline is represented by Keen Sense, Mirri the Cursed, Crovax, Ascendant Hero, and Kor Dirge.
The third is a timeline where a whole bunch of Otaria characters are color shifted: Braids doesn’t work for the Cabal, Akroma is red instead of white.
Another timeline where Tocasia was an elementalist instead of an artifice archaeologist.
Another timeline where Jedit Ojanen stayed home and was loyal to his homeland of Efrava.
Another where Serra’s Realm was populated by Sphinx instead of Angels.
Another timeline where the Primeval Dragons are different than they were during Invasion.
There isn’t a whole lot of “why” for any of these. There might be more I didn’t see scrolling back through the set. If you know of more, let me know.