Mogeko Castle Gaiden: "General Hashasky's Great Adventure" is a game that Mogeko (Deep-Sea Prisoner) is planning to make. This game might be decided to be made or canceled (Now, now before you say something mean to our god, yes it is 2018 and it isn't released yet, YES I'M FUCKING TIRED OF WAITING but let's all respect Deep-sea prisoner and wait patiently a little bit more). Before y'all freak out, the reason behind this is that there are some other games that Mogeko has also planned and is developing: Carnival Rhythm and The End of the Wonderland (if anyone knows anything about the progress of those games, then mention it in the comments as then we might get an idea of how much longer we have to wait). The trailer can be seen in the end of the game and in the Bonus Room.
On the 11th of July 2018 YouTube user RozenKrieg uploaded an unlisted video showing the start of Cannibal Rhythm and Mogeko Castle Gaiden. On the 8th of August 2018, user Mogekov Hashasky also uploaded footage of Gaiden.