I know it's Gelgoog, just not which specific variant this is

Going by the artist's twitter, I think it's supposed to be an heavily tweaked ReGelg?

basedheero said:

I know it's Gelgoog, just not which specific variant this is

It's no official variant. The backpack is from the Doven Wolf, the shoulders are modified ones from the ReGelgu, the head is new and the chest likely too.

Gelgoog III? From advance of zeta?

Rocko1345 said:

Gelgoog III? From advance of zeta?

Head definetely seems to be a Gelgoog III based on this image, though it's not the same torso

It's a kitbash, got it. :P