Seraph raises towers which serve to funnel light to her palace, they don't terraform but "drain light" from adjacent areas creating a variety of interest effects. We WILL be revisiting the core six Old Ones to see if terraforming abilities will benefit their strategies and theme but Inatha and Moloch are the only two who pivot around terraforming abilities as they were two that were specifically stripped from consideration early because the static map wouldn't support them.
Inatha is straightforward - a combination of slow but permanent conversion to tundra as well as the ability to push out sudden storms and other environmental effects from the mountain peaks that still contain his voice. Moloch is more insidious and open to various approaches from forcing the hexes adjacent to his pools to regress to a primal state (jungles, high temperature, more danger) to corrupting rivers with his bile forcing downstream POIs to suffer to wielding his tendrils like weapons to form massive wounds in the earth permanently damaging the hex (and any POI atop it). However, each usage provides openings for the Heroes to descend into the Underworld and seek out his Heart, or at the very least sever some of his tendrils.
I'm hoping we get to another Old One vote (though Race is next) while in Beta as one of our next contenders is a Sentient War Machine from the Age of Wonders that has a very unique relationship with terraforming focused around ancient ruins, though I do expect Tzadar to rally and take it.