What you were expecting to happen, and what actually happened?
Gorgotha summoned a Giant Spider and not an Ancient Horror
What are the steps to make it happen again?
first time that I’ve encountered it.
Do you have any screenshots or video you want to share with us so we can see the problem? Attach them to your post!
Sadly I didn’t not take a screenshot when Gorgotha summoned the Giant Spider, but once I killed the Giant Spider a Gorgotha came back as the game ended.