Found another problem: if Embers of Rage isn't enabled, the addon chokes trying to modify the nonexistent Miasma Engine talent. Which I guess wasn't a problem before you added the Golem Rider evolution. ;)

Another thought: you make a point of refunding the talent points spent in the Steamtech/Mecharachnid tree when the player takes the Mecharachnid Rider evolution — but Steamtech/Mecharachnid is a locked tree for Annihilators, so the player is also spending a category point to unlock that tree, and that point isn't being refunded. Now, I could see that cat point being considered part of the "cost" of the evolution; if so, though, I'd encourage mentioning that explicitly in the description.

(Oh, and as a complete non sequitur, there's already precedent in the Mecharachnid Piloting talent for displaying the mecharachnid tile on top of the player tile, and I think it would look cool to use that for this evolution too.)

So, this looks fun, but… one of the requirements for the Mecharachnid Rider prodigy is "invest 5 points in Mecharachnid Rider" — and I can confirm that no such talent exists, by that name or by the T_MECHARACHNID_RIDER talent ID you use internally. I'm guessing you meant 5 points in Mecharachnid Piloting?