Speaking of Jurokubei, I have a tinfoil hat theory that he was originally suppose to be in Mystical Ninja: Starring Goemon. Let me explain:
So you remember these certain ninja enemies from Ganbare Goemon 3? The ones you see in the thumbnail right here next to Bismaru:
They were originally suppose be in Mystical Ninja: Starring Goemon as they were in some old images here for the beta:
It's interesting they were in the beta. And you know what else is interesting? Goemon's Impact costume from Goemon's Great Adventure is in the first image above. What does this mean? It means Great Adventure used some assets from Mystical Ninja and not just finished assets but likely beta assets too. And it's quite interesting Bismaru was in Great Adventure but not Jurokubei or the any of his other minions from Ganbare Goemon 3. What if Jurokubei and Bismaru were originally suppose to have been in Mystical Ninja: Starring Goemon and the Bismaru model in Goemon's Great Adventure is the same unused Bismaru model they made for Mystical Ninja: Starring Goemon? It might sound farfetched, but with the ninja enemies from Ganbare Goemon 3 originally in the beta and Goemon's Impact costume from Great Adventure in the beta as well, it gives my theory some credibility.
And you might ask, but why would these guys be back for Mystical Ninja: Starting Goemon when it doesn't take place in the future? Well here's your answer:
In these beta screenshots here, you can see Impact chasing a cowboy robot in what looks like a modern city in the future perhaps. Perhaps parts of the beta in Mystical Ninja took place in Jurokubei's time period in the future which explains why we see his ninja minions in some of these screenshots. But didn't Jurokubei redeemed himself at the end of Ganbare Goemon 3? Yes he did, but Bismaru was still on path of evil as shown in Goemon's Great Adventure. These ninja enemies were probably only loyal to Bismaru and not Jurokubei which is why they're still enemies in these screenshots.
Jurokubei could have been a great assistance to his ancestor if he was originally in Mystical Ninja as he could have played a similar role to the Wiseman in someway or maybe he could have been playable in some parts of the game as it might not be too farfetched since he is the descendant of Goemon the main protagonist.
But that's just my theory that holds up some credibility because of these beta images. I truly believe Jurokubei and Bismaru were originally intended to be in Mystical Ninja: Starring Goemon and Bismaru could have been the main antagonist instead of Dancin' and Lily. And since Bismaru was the co-antagonist in Goemon's Great Adventure, this isn't too farfetched at all. What do y'all think?