If you don't want to read through that whole thread, the answers to unlock a variant have also been posted on Handelabra's website, at http://sentinelsdigital.com/variants.html
The above link will always be updated as soon as the community figures it out. The Devs watch our efforts to figure out variant unlocks very closely, and even give a hall of fame spot to whomever figures it out first, so if you don't want to take part in the discussion yourself, the above link is the place to look daily until any variant is figured out.
If you're talking about unlocking the Rook City variants, there is a thread for this in the forum for the video game: https://greaterthangames.com/forum/topic/unlocking-rook-city-variants-spoilers-7206
If you don't want to read through that whole thread, the answers to unlock a variant have also been posted on Handelabra's website, at http://sentinelsdigital.com/variants.html
The above link will always be updated as soon as the community figures it out. The Devs watch our efforts to figure out variant unlocks very closely, and even give a hall of fame spot to whomever figures it out first, so if you don't want to take part in the discussion yourself, the above link is the place to look daily until any variant is figured out.