Hi, thank you for taking such enormous interest in our game! We are happy and humbled by the thought you put in our game.
That's a nice fitting idea with creature gallery. We base the game on creativity and that would encourage it even more. This could also tie nicely with some kind of sandbox mode you've also mentioned. So far, our plan is to release the game with campaign mode only.
The game is still in development and only the first boss is mostly going to stay the same. The rest are going to be tweaked to follow the right difficulty curve. We occasionally change balance of the game, trying to find the right spot for pacing. For now, the game is in "Harder Mode" for earlier levels. We'd like to push that difficulty up to higher levels.
Multiplayer is a big topic and a big undertaking for us and the game. We didn't plan it initially as it would require to already have a substantial playerbase and more time to develop. We would like to release the game with solid base mechanics and singleplayer mode first. After that - we will have to decide if future of the game would be better with more singleplayer content or a multiplayer mode. We can guarantee that the game is coming out with a campaign mode as seen in the demo.
Once again thank you for ideas. We appreciate players telling us what they like and want in the game because it allows us to focus our attention on the right things. Cheers!