Allright, I have some news on my progress:
To start with, here's the new WIP:
http://dehacked.2y.net/microstorage.php/info/483/Advanced%20Dungeons%20%26%20Dragons%20-%20Heroes%20of%20the%20Lance%20%28U%29.fcm
As you can see, it's almost identical, here's what I've come up with so far:
It's not possible to duck under the shot from the first green fish guy, since the shot is too low, I can't jump over it either. So I have no choise here but to get hit.
It IS possible to duck under the shot from the second green fish guy, but this is exactly as fast as getting hit. So at first, I ducked under his shot and continued the run. But I found out that how much HP you have is a huge factor for monster behaviour in this game. As you can see in the WIP, I can enter the door in the following room before getting hit by that shot. If I duck under the shot in the room before, the third green fish guy will move slightly differently because I have more HP, and I will not be able to make it to the last door without getting hit. If I get hit by this lizardman's shot, it costs me 2 frames.
So the two choises are either to duck under the first lizardman's shot and get hit by the second one, or to get hit by the first one and avoid getting hit by the second one. The first technique is the fastest, so I chose that.
Another thing you might notice is that around frame 4900 I don't get hit by the green enemy. I found that if you run towards him, turn back, and start running towards him again, you will run through him, you will see what I mean when you watch the WIP. This neat trick saved 9 frames. Unfortunately, there was a flaw with this trick too. Since this made me loose less HP, some enemies behaviour changed.
You know the room where I jump three times to avoid the arrows to appear? Well, it seems it's not possible to get the arrows to disappear this time, because my HP is too high. So get hit by one of the arrows. This lost me 4 frames, so I'm currently 5 frames ahead of my previous version, wiiee!
Maybe all of this was a little confusing, but to put things short, my problem now is that I can't get that arrow to disappear, the one around frame 6000. If someone could do something, like jumping at certain places or something, to get it to disappear, I would really appreciate it, otherwise I'll continue from what I have so far.