Re 1. It's worth mentioning that this is actually the second attempt at making this game. My first attempt was 9 Till Void, which is available on my itch or steam and has similar mechanics but with some tweaks and some things missing (there's no XP or Gems in that one). This game came about from finding the original prototype of that game, which looks a lot closer to Ennead, and realizing "Wow I think I like this prototype more than the thing I actually released? Maybe I should try this again..." And in those older versions there are more enemy types, including an enemy that blocks the spell in its row from being used. I definitely am open to adding more enemies, but in past experiences it's really hard to get players to mouse over enemies to understand what they do, and also players generally dislike really disruptive enemies. The demons in Ennead work well because its so easy to understand them. I'll think more on it though!
Re 2. Yes I can definitely improve this. To clarify how it works, Void gets created at the end of your turn if Turns is at 0, and Void deals 1 damage to any entity at the end of its turn. The damage is dealt before void gets created, so if you move to a cell which will become void at the end of your turn, it wont hurt you. So just be mindful of ending your turn in void that exists right now, and also consider how enemies might end their turns in void too. I can definitely improve the visual on this. I could also maybe simplify it to make everything happen at the end of your turn to remove some ambiguity, it would just change the balance in some subtle but impactful ways since damage would be applied to enemies before they move instead of after.
Re 3. Streaking actually might be a good way to introduce more enemy types. Restrict more disruptive and complex enemies to streak difficulty modifiers. That would work well I think. I'll have to think more though because I honestly don't like the streaking aspect of brough games, usually. I personally prefer when a run can exist in isolation. I do want to provide some new challenge after players win though that isn't just "get a higher score" so I'll see if I can come up with a non streak solution first, but I'll keep streaking in the back of my mind.
Thanks again for the comments! I'm not sure how soon I'll get to updating the game, but I'll make some devlog posts if I do, so be on the lookout!