Hey there! I came back with some news.
I'm working on the new game mode - it's gonna be a kind of Campaign mode. Instead of enemy castles, there will be enemy machines that lauch enemies. Once they are completely damaged, the enemy boss (which is likely to be random, but I'm not sure about this yet) will fall from the machine, and swallow the jewel, and they say something, like "If you want the jewel you've got to defeat me first!", and once you defeat it, it'll explode and the jewel will fall to the ground, and then you get to destroy it.
(some machine concepts are in the screenshots; sorry for the quality and for the finger in the picture, I'm really in a hurry)
Also, the campaign mode will have a world map, so you know how much of the game is left until you finish it for good
(until you reach Cthulhu). It's also in the screenshots. For every stage you complete, the ambient will change. You'll start off in a beach, then go to the forest, then to the desert, plains, and finally, mountain. I'm actually not pretty sure as for keeping the mountain as the last level for Cthulhu raises from the ocean in the original story, so the final stage might actually be in a boat, in the middle of the sea.
I plan on making new soundtracks for each stage as well. You'll have news pretty soon, guys, so keep visiting my devlog. Also, your favourite is REALLY importante to me; if you don't mind it, I'd ask you to favourite this project so more people get to know about it. Thanks for the support! ;D