Great concept. I think what works particularly well is your implementation of the poison mechanic. It's an ever-growing threat, but its rate allowed me to make (or at least feel like I was making) informed decisions about how long to stay in a certain room or where to go, which is preferable to the "get here or die" approach of other games.
The only thing I'd change is to either make the other slimes faster or slow the player down to increase the chances of being stopped. I made it a point to keep moving rather than linger in one spot or area, but I only ran into two or three over the course of an entire round.