This was fun! (got to level 8!) I liked the character and UI art! Something funny is that I actually used the same soundtrack by Matthew Pablo in a game I made for an Open Game Art Jam some years ago. It's great to see the track used so well and getting more exposure!
I enjoyed the vampire survivors-like gameplay. Having upgrades even with the 4-day time constraints was really the cherry on top. Shotgun felt like the strongest ability, since the extra shot combined with the regular bullet took out 2-shot enemies quickly. Booarang was also cool because it functioned similarly. Shurikin was fun because you could use skill to ram it into enemies, but it didn't feel powerful enough relative to the amount of effort needed to use it. Would also be cool if you could get a shrunken that spins in the opposite direction later on. Though I think it's alright for things to be a bit out of balance for these types of games, because a lot of the fun comes in finding the OP strategy.
I didn't notice the player character strengthening when the time got lower. If his damage gets higher, maybe adding damage numbers flying off enemies when they're hit would make the player notice it more. I kinda wish the time crystals had bigger collection areas, though that might just be a skill issue on my part. The movement felt like it had around a 0.1 sec delay before it responded to the keyboard, which might be because of lag on my computer.
The enemy variety was awesome. Each enemy felt distinctly different, presenting its own challenges to the player. I never got to meet the cat boss, but I might come back and play the game again later to beat him.
This is a wonderful game! Great job!