How does it work when you get paid for deriving from a copyright piece of material in the first place?

Since the artist was commissioned by Bungie to make the original concept art in question, I believe that Bungie still retains ownership of the copyright, since the work was created under Bungie's employ.

That said, it's not uncommon for these types of commission contracts to stipulate that the artist retains some rights to the works they create. It varies from contract to contract, though. Sometimes they just require that the original artist is credited in any further usage of the piece, sometimes they require the artist earns royalties from any sales of the piece, etc. Or, he could've also just taken a fat stack of cash for zero ownership, which isn't totally unheard of.

So, to be fair, you're paid for your service of creating the art, not for the copyrighted material. I would think that is different than to creating a piece based on copyrighted material and then selling the finished art. Anyways, Bungie does not get ownership of their art, just the ability to sue for profits they make from selling it and/or damages, at best, If they can prove it violated copyright and it is not transformative/under fair use.

Also... while I'm here... god why white and orange it looks so bad, doesn't match what is in game, and just... no.

as the tweet says and as you would see if you actually compared them, the nerf gun literally has the exact same details on most of the design, especially the diagonal stripe is literally the same fucking asset.