Diablo 4 season 3 has 2 new Uber Uniques for your companion that will give you 'bragging rights' if you can find them
Everyone in Diablo 4 season 3 will get their very own robot companion that you can equip with all sorts of powerful skills and then modify with «tuning stones». You can read through a list of these new seasonal items in Blizzard's blog post, but two of them are left blank and said to be talked about «in hushed whispers» by Sanctuary's scholars.