This was really fun once I got past the very beginning. Starting immediately was a surprise and then figuring out what to do first made me die 2 or 3 times.
Once I figured out what to do and to stay pretty far away from the beginning enemies then I was able to get a few weapons very quickly and things got a lot easier immediately. This is when it really started getting fun, running around taking out little slimes or whatever they are. But then the lions and birds showed up and it got more interesting. More cool animals showed like a gorilla; I liked that a lot. Then after like 10 minutes or so it got a bit repetative what with the music track and kinda doing the same thing over and over. The hidden grass collisions that you mentioned didn't help either, but understandable for a jam. Also the scrolling level seems very slow to graphically refresh and kind of hurt my eyes a bit when trying to concentrate on it while moving around. It may be the laptop or screen I am on so I will try it on my desktop sometime too, but this laptop is pretty powerful so I don't think that is the issue.
Very cool concept overall and it was very enjoyable to play! Is the level procedural or one big map that wraps around itself?