Here's one of the new levels from Chapter 4. It includes Slimy Slugs, which leave a deadly trail of acid slime, and Sniper Snails, which as you can see in action here, spit a stream of acid with (not so) great precision from long range. If you get in close to a Sniper Snail, he'll hide in his shell, invincible, until you move further away. That makes them nice and annoying.
This level is actually called Gastro-Pods, because it contains those pods you see (the bluish walls) made of slug slime, which you pop open with switches. Yes, it is the last level I made, and that's the most creative thing I could come up with at that point. I'm just glad it's done! It's a pretty fun level regardless, and it takes some skill to stay out of the slug trails and dodge the sniper fire.
The snails and slugs are the two new enemies I'm really happy with - they both turned out exactly how I wanted, right off the bat, as soon as I finished the code. I hit compile, ran a test level, and was laughing and enjoying them right there. The best is the infuriating way the Sniper Snails hide from you. Oh, they'll make you mad.