Just to clarify this: The Extra Thicc Edition DLC includes
wallpapers, artwork and avatars.
You also get the game's
full soundtrack, which includes tracks you won't find on
Akhzul's Hedon OST on Bandcamp, since that one only includes Akhzul's work. The Thicc Edition soundtrack adds all the licensed songs by artists like Alexander Brandon, Breathelast, Methadone Skies, Doomnezeu etc.
You also get a
new optional HUD which was designed to look like the kinds of overblown HUDs you'd see in old-school dungeoncrawler RPGs. If you have the DLC, you can activate the HUD in the menu and then switch between the new and old HUD using the "increase/decrease HUD size" keys.
The Thicc Edition does not change anything about the gameplay, however. The release of this edition coincides with the release of update 2.2, which does add stuff to the base game, but you don't need to buy the Thicc Edition DLC to access that content. The Thicc Edition is mainly for people who want the goodies described above or want to support the dev (keep in mind that Zan released the entire second episode as a free update to the main game).