Awesome job! Loved the new bosses, new moves, and startup mode. And i tried to play local co-op with my bro and it was amazing!
I think you can do something more. For example, you can make a proper online mode with different game modes like pvp or co-op up to 4 or 8 players. In that way, people could host a server and play with their friends while being far away from them. And maybe you can use the "under construction" space for the "online mode" at the main menu.
I believe you can make this game even better. Have fun out there, good luck!