Oh crap! I wish I had known about the mutation because I think it was a really cool idea to make it diagetic.
I was too focused on trying to get the code right and assumed I had to complete the game before getting overrun by zombies. So I ran past all of them until I found the right code but the rooms were full by then, haha.
I appreciate how it feels like you're trying to give players the fun of discovering the mechanics for themselves. If you're taking suggestions I would say that players might be nudged to killing enemies and thus realising their mutation and it's effects if you made the feel of shooting them 'juicier'. Like if the bullets were faster or hitscan, the fire rate was improved, blood splatters on hit and enemies stagger to the shots though I understand how the time limitation could've kept you from doing more. The monsters spawning in the same room I'm in also discouraged combat for me as there was no vantage point I could use and it felt hopeless to try and kill them off.
Went on for a bit there haha, but I really like what you were going for. :)