Are there too many enemies generated at later levels? I compare with the video walkthrough - there are much fewer of them.

https://youtu.be/Er-9iy6U4Hg

Probably use Segment 0 for the RND?

I think is not needed, the used range contains program code, what can be done, to change it to RND code, for example to István's quite short RND code.
Should i try that solution?
But there is no guarantee that similar situation is not occur.

Maybe you could do an X-Y plot test to see if using István's PRND produces hot spots in this program.

It is a good idea, just it would not be valid, because that RND uses also register R, and it should be used in the same place where the game uses it, but i can try it in the game, and put values into a non used memory range, and we can check how often were placed sprite into the same position also. I will try it.

I think it should be done in the debugger with scripting. Wherever you call the original PRNG trigger a script that calls István's generator (obviously implemented in lua) and collects the data. Do some (a lot) rounds in the game and evaluate the data set.

Levels with many rats (3-5) in one place I met very often. Even in tight places.

I think there is no problem with the number of the rats, and any enemies, just with the distribution.
I will make a test with "original random" and IstvánV's random to check which works better by filling up empty memory area and check which looks better, and solve avoiding to put more objects to the same place.

Acid drops has too wide hit range.
Is it possible to fix this?

Attribútum módban a legjobb! A többi módot el is lehetne felejteni a játékhoz. Ennyi szín és ilyen nagy felbontás egészen szokatlan, mintha nem is Enterprise lenne. Ilyen játékokat kellene még írni. Ilyen grafikájú játékhoz kellene majd olyan zene, ami jobban kihasználja a Dave képességeit a szűrőkkel és gyűrűmodulációval. (Ebben a zenében itt nincs ilyen, de legalább a basszus Dave-es, és sztereó is.)
Az elhalálozás idejére a zenének meg kellene állnia, mert az elhalálozás zenéje más hangnemben van, mint a játék közbeni zene, így fülsértő, hamisnak hangzik. Esetleg összedobhatok valami, Dave-t jobban kihasználó elhalálozós zenét, ami majdnem olyan, mint a mostani, csak kicsit Dave-esebb.

Acid drops has too wide hit range.
Is it possible to fix this?

I will check, but as i remember it checks if a character in a specific position contains any nonzero value (in 8 row), and if contains then it cause collision,this col16 mode has 6 character wide objects, fred is also 6 character wide, but if i remember well we can go through acid also without damage.
I will check the possibilites, but i do not give too much chance for it.