You think, that Bubsy 3 "No More Mr. Nice Guy!" is the rarest media from Bubsy? Well apparently, Michael Berlyn tried to make Bubsy 4 after Bubsy 3D. Or did he?

There are only two articles about it. The first article confirms the existence of it:

"We learned a lot about 3D design and coding and the environment and what could and what couldn’t be done," he said, "and we went to Sony to pitch them on doing a product. We brought a prototype for Bubsy 4, which was really just nothing other than a calling card. And they could see where we had taken it, and said, 'Oh yeah, we’d be interested in doing a product with you. Absolutely not a furry animal product, though, we already have one of those." At this time, the Sony marketing machine was busy placing their new mascot, Crash Bandicoot, into pizza commercials. "So we said okay, pick a product any product, and by mutual consent, we agreed to do Syphon Filter." Syphon Filter, a 3D action game obviously inspired by Metal Gear Solid, would prove to be Berlyn's last.

- Gamasutra, 2005

The other article declines it:

Josh: As the legend goes, you sort of got pulled into Syphon Filter as you were trying to pitch Bubsy 4. Is that true?

Michael: I pitched two other products that were not Bubsy. One was called Sparky and Bolt, which was an electrical boy and a sidekick who was a dog, who was electrical also, in kind of a Jetsons future where appliances had come to life and were attacking the city. Sparky’s goal was to kill the enemies, and Bolt would act as a sidekick and recharge him and shoot lightning bolts out of his nose. It was a very well-developed concept.

Josh: Yeah, that sounds really fun.

Michael: I pitched it to Sega, and Sega said, “Not enough edge. Have Sparky be a punk with an attitude, and have Bolt be some sort of nasty cat or something.” And I said, “You’re missing the point.” And I guess I was the one missing the point, because they turned it down.

I pitched it to Accolade, and Accolade said, “Ummmmm, I don’t think so. We’re more interested in a Bubsy 4.” And I said, “I really think Bubsy’s dead by now. Between what you guys did with Bubsy 2 and What I did with Bubsy 3D, it’s time to move on.” They didn’t agree.

At the time, Sony was making noises about wanting to buy the development company, and I had just left it. So Bubsy 4 was not a possibility, and Sparky and Bolt never happened, and Dingo Dan never happened.

- Retrovolve, 2015

Sources:

https://www.gamasutra.com/view/news/97672/Playing_CatchUp_Bubsys_Michael_Berlyn.php

https://retrovolve.com/a-chat-with-bubsys-michael-berlyn-part-2-rejection-and-reinvention/

(found by Polimpiastro on Reddit: https://www.reddit.com/user/Polimpiastro/)