The main change is the addition of another new race: Dinosaurs. It's named Temple.
With a new city and its own new units – different types of dinosaurs.
You can see the new city and the new Dinosaur race on YouTube; the video is titled "Heroes 7.5 Preview update 1.26".
The link remains the same as in the first post.
I have updated the post to version 1.26.
There are 2 files there: the mod itself – Heroes_7.5_version1.26.zip,
and a separate file with the Xel and Dinosaur (Temple) races – Heroes7.5_Temple_and_xel.zip.