Finally got around to playing your game. I saw you showcase it a bit ago in the PGC discord. Wanted to play it since you showcased your boss fight.

I know there's a brief introduction on the itch page, but a simple introduction like in Undertale would do wonders. Players just picking up the game might be a little lost. The title screen art is very nice though.

Minor nitpick but the theme music is a bit amateur sounding. I've been trying to get over this myself so maybe I'm projecting it on an otherwise good song, but to me a LOT of indie game music starts with something, then another layer comes on.. etc. It was just very noticeable to me. (Aside from the theme, all the music seems fine, and doesn't get repetitive)

I have no idea what I was reading in the starting area, I'm assuming it was a map? But it was moving to different sections or something. Perhaps I'm not supposed to know what it is initially.  (Oh I'm reading the full itch page now, it's for customizing the mine.) I know it sounds stupid, but I'm willing to bet I'm not the only one who doesn't read the whole itch page. Just something to consider for a lot of aspects. Also the customizing is still confusing.. maybe I'm slow.

Mining is a fun mechanic, some subtle feedback with it. I like the boss talking sound lol. Good enemy diversity. The enemies seem smart, I think? They appear to hide, or run if they're low on health? The enemy knockback and stun is brutal though. Getting caught in a tight spot with enemies on two sides of you is HARD. Drains your health.

Wow this game is hardcore. At first I thought I liked the difficulty, but now that I'm putting some serious time into it, it kinda feels like it prevents the player from experiencing the game unless they sink serious time into it. imo, an indie game like this, I think you need to do more quicker to keep the player's attention. I'm not sure what that is, maybe closer resources, cheaper costs? I don't know. My current problem is most runs I don't find one resource, I have no idea where to get it. I like that I can't breeze through it, but also I feel like I'm dying before I really got to do anything. I'm on my third life so maybe it'll get better. It took until my fourth life until I found julite, maybe it's my fault for not exploring far off enough. I never found the middle black resource in all five of my runs? lol. 

It seems even with upgrades it's pretty hard to handle the onslaught of enemies from every direction. Training is my go to strategy. Maybe I'm fighting them positionally wrong. Holding left click and using WASD to weave in and out is what I've been doing. Even something like a little bat rekts me if it's behind me. Maybe only certain enemies should have knockback and stun? lol

I think with each shift you're making the difficulty harder? I'm not sure how I feel about that. I feel like it negates my upgrades and I can't keep up. It seems like the enemies even start to reject my training by going to the opposite side of the room as me to shoot projectiles. Smart enemy design.

I only found one bug, a bomb flew across the map to me lol. I was on shift 6, trying to get one more upgrade, and then I died. So I decided screw it I'm doing the retire boss fight with no upgrades. VERY cool boss fight. Also very hard. I have no idea how to avoid his laser lock on attack. Died a bunch. I played five lives. One thing I want to add is this game is very dark and tbh does get a bit "samey" after a long play session. When I found the julite room it was like I emerged from a dungeon, finally color! Kind of light!

These are just my thoughts on my first session. I may return to it. You may take my criticisms on the balance/difficulty with a grain of salt if you'd like, but I think I'm above average in games usually for reference. I'm assuming there's two endings, shift twelve and retire battle. This game is definitely polished though. Feels like any old indie title. Good job!