The ending we see before the credits and the ending we see after the credits are not the same ending. When they entered the time portal their timeline split in two creating two parallel realities. In the first reality (the one before the credits) Griffon and Nick are separated and spend eternity alone.
In this timeline Nick becomes Busto1.0. He knowingly sacrificed himself to save reality and upon becoming Bust1.0 he goes back to the time before this all to try to warn past Nick and Griffon about the dangers of the blob and prevent this all from happening.
In the very same timeline, Griffon wasn’t given a choice about sacrificing himself. (as learned in the second timeline) and as such never had a chance to say his goodbyes to his loved ones like Nick could. Stricken with this grief and loneliness Griffons chaotic side slowly eats away at him and turns him into Busto2.0.
If you recall to the fan-animation “Car Boys Animated - Some Sort of Digital Heaven” (which was stated by Polygon as being canon) at the end of it you see Busto2.0 opening his arms to welcome and embrace Busto1.0. That's Griffon being reunited with Nick.
Which leaves one finale question. Who or what is “Busto3.0” aka The Blob? Well little is known about the blob, but if following the pattern of how the Bustos are created, then it can be assumed that the Blob’s origins are similar. For starters lets talk about what we know about the blob. 1) It hates water. 2) its physics are fairly complex. 3) There are people who love it, and more specifically Griffon is one of the people who has to constantly fight against his love for The Blob.
Now then who fits all three of these points AND was brought into the time portal with Nick and Griffon? Ball. Ball would constantly spring out of any water it was put in. Ball has a very similar level of complexity to its physical properties. and Griffon absolutely loves ball. Both of them do. Everyone loves Ball. In fact it was Griffon’s love for Ball that created The Blob. When they were entering the time portal Griffon stated, “I’m scared, can I have Ball? I love ball! ” To which Nick complied and brought Ball (as well as The Blob) into the time portal thus damming them to a repeating cycle.
Ball was dragged into the portal and as a result ended up getting stuck their forever, Griffon didn’t like seeing Ball be trapped in forever and they were forced to leave ball behind. Thus, just like Nick and Griffon, Ball was left all alone for eternity thus forcing Ball to change into The Blob. Who only ever tried to reunite with the boys, but in its changed state, it ended up consuming everything.
After all, the Blob itself wouldn’t hurt the boys and as Griffon said “-if it detects malice… it will activate the protocols ” meaning it only attacked them when they attacked it first.
Now I could be looking into this too much, after all its a video game series about two good soft boys playing a physics based car game. But they did such an amazing job creating a whole story around this series, it only seems fitting we continue to honor it by having these overly complicated theories of our own.