There is a save system! You have to press ESCAPE while in game, then hit save and choose a save slot. You will need to reopen the game to load a save though. With the new version, there will be more info about menus.
I have thought about a demon race and it will for sure come sooner or later. The next one will be Orc. After that, the focus will be on implementing all growth stages which will be 10 in total. With that done, a new race will come every 1/2 updates. Races are really easy to implement it is just the renders need to be done, which is what limits releasing them frequently. If you want, I would be glad to see a description for a demon race! If you have any other suggestions, you can either comment here or contact me on discord (faustto), which I check more often.
By companions do you mean the NPCs? They grow even at the current version! It may be because of the bad explainantion of how to play the game, but there is a little story with interactions and fights too, which do involve them growing.
I have watched a few videos of Spore and having very strong enemies is indeed a great idea. There is something simmilar coming in future updates, which is more like a boss, which you will need to outgrow in order to defeat. I will think about making something like that.
More enemies are coming! The main problem, because of which there are only 3 right now, 5 if you count the bosses, is because sprites for enemies are hard to make and the artist I comission works quite slowly. I am now having them reowork the sprites for the old enemies, after which I will implement 1-2 per update, some of which will be much stronger as the current ones are 'Tier 1' opponents.
As the game is focused on pixel art, the current lakes do a great job. Making them circular will be very hard, as it will involve making a pixel art shader, which is very hard and I don't think it would make the game better in any way.
If you have any other ideas, feel free to share them either here, the game's discord server or personally to me!