This isn't guaranteed to fix it for 100% of people, but should resolve it for majority
Please follow every step in order before reporting back.
Why this happens:
The game loads your patch files in order (patch, patch-1, patch-2... patch-5, etc.), and each newer patch can override data from older ones. Ddosy's pet model was added in Patch-5. If your install still has old, unused files like Patch-6 through Patch-A left over from a previous version, those get loaded after Patch-5 and quietly overwrite the info the game needs to find Ddosy's model, even though Patch-5 itself is completely fine. The pet still "exists" on your account (that's why the game says you already own it), the game just can't find what it's supposed to look like, so it shows a placeholder cube instead.
Step 1:
Fully close WoW and the launcher. Not minimized, actually closed. Windows won't let you delete files that are still in use.
Step 2:
Open your OctoWoW install folder → Data folder. This is wherever your launcher/shortcut installed the game (Desktop → OctoWoW → Data by default).
Step 3:
Delete these files if you have them:
Patch-5.mpq
Patch-6.mpq
Patch-7.mpq
Patch-8.mpq
Patch-9.mpq
Patch-A.mpq
Only delete these exact files. If you don't have Patch-6 through Patch-A, that's fine, it just means you don't have the old leftover files.
(The Picture shows how your data folder should look like, Patch-0 is optional as its Raid Visuals)
Step 4:
Delete the WDB folder. It's in your main install folder (not inside Data). This is just your local cache — safe to delete, it rebuilds itself automatically.
Step 5:
Open the OctoWoW launcher (not the game yet) and let it redownload Patch-5.mpq. Let it finish completely, don't close it partway through.
Step 6:
Run "Verify Files" , to double check everything downloaded correctly.
Step 7:
Launch the game and check the pet. Open your Companion/Pet journal and summon Ddosy directly from there, don't use the item again, since you've already learned the pet.
Step 8:
Still broken? Create a GM Ticket or ask for support on the forums here. Please share a screenshot of the data folder. (as referenced below), so people can see what files you got. Please don't just tell us "it's a fresh install"
Several people who said that still turned out to have old Patch-6 through Patch-A files sitting there.
I will try and troubleshoot as much as i possibly can.