The HeroClix stuff has been going on for decades so I'm betting there is one out there. Maybe Doomscribe just didn't include it in his photos.
I probably saw this at the time but after doing some googling I found out that Terrax was a Marvel Legends Build A Figure from 2016 where you had to buy a whole set of other characters to put it together. Here is a link that shows all the figures you had to buy (usually it's 6) and how Terrax looks once you put it all together.
I never have gone that route. Maybe it's because they wanted to keep the figure at the right scale to the others but it's also a cash grab for a really serious collector. And I've seen those on YouTube where they have an entire room dedicated to displaying them.