Since this is a DOSBox problem, it should be in the DOSBox forum.

Anyway, it's quite possible that on the original hardware the game also ran at a crawl and that destructible walls also blinked. There are other ways to run old DOS programs (like PCem or Bochs or perhaps VMware), but they are not nearly as easy to set up as DOSBox and probably won't solve the problem.

Why not just get Megaplex, as suggested at http://elmerproductions.com/sp/faq.html#q_xp ?

thought it ran correctly in 0.74.

are you simply running SUPAPLEX.EXE, or are you using the latest SPFIX provided on that site? if you aren't, you definitely should - it specifically addresses the speed issue (and fixes some other bugs too).
I actually finished the game with it, so it definitely works fine under dosbox, just like on real hardware.

http://www.elmerproductions.com/sp/faq.html#q_whyspeedfix

[EDIT] forgot to mention: if your monitor supports 70Hz refresh rates, you might want to set your video mode to that, since the game relies on it for smooth scrolling. Still perfectly playable without it though (this isn't what's causing your problem).

I'm using spfix63.
It's definitely slower than the original speed.

[Thread moved to DOSBox Games/Apps. Section]

Have you tried any of the other suggestions in the FAQ?
http://www.elmerproductions.com/sp/faq.html#q_changespeed

Too fast or too slow? a little confused by your two different posts. For reference, this video shows the original & correct speed - http://www.youtube.com/watch?v=ZD1C4pnYhQs

the original SUPAPLEX.EXE ran too fast on a 486 or better, so your original experience may differ. (Most Supaplex videos on youtube don't seem to have the speed right, either)

I believe it should be too fast on dosbox by default so overall it is too slow.

.... if you believe it "should" be wrong by default, but DOSBox insists on getting it right, just try spfix's command line parameters to force a different speed (see the docs).

That's what I did. At first it plays proper speed then but then slows down to a crawl.

Hmm... While I haven't really played a lengthy Supaplex session for some time...

I recall the following command has made it (improperly) fast as I originally experienced it (and for sufficiently long time):

1spfix63 *0

With that, as you load a puzzle for the first time, it may be slow for less than a second, but then the speed should be "auto-corrected".

Oh, some speed-related DOSBox settings might also have their own affects. Here are ones currently used here, although it may help if you play with these:

1core=auto
2cputype=auto
3cycles=max
4cycleup=10
5cycledown=20

In fact, if you've still got problems with the spfix command, I may suggest to try "core=normal".

As some have already mentioned, while it may feel like the speed I originally played it with, it's not the "intended" one; In particular, if you want to make any comparison with one of these scores posted online, then the intended speed is the only way to go. (...Or is it?)

Well I tried the settings and it's the same.
In the original supaplex video the walls were blinking too so maybe it's just emulating the original, idk.

http://www.youtube.com/watch?v=t75H_L2oGuE
here's a sample of my supaplex speed, still seems slow.

Guess the problem is you got used to it when it was playing too fast on your real computer. The program accepts command line parameters though.

I used to play Megaplex instead of Supaplex, and it's faster at 35 fps.

Well, it is faster for me with "spfix63 *0". So, I think it'd help if you tell some more info:
- If you've still got the Supaplex download, is it a file named supaplex.zip with an exact size of 294017 bytes? (It'd be even better if you can check its md5sum is 50643570a58c8f13a79d49eab199aba8.)
- Knowing that other DOSBox users had mistakes regarding that: Are you sure you're editing the correct DOSBox configuration file? (e.g. when you edit it, things change in DOSBox?)
- Post the contents of the configuration file (as an attachment).
- Also tell the exact commands you type in DOSBox (mount command, directory change...), in order to load Supaplex with some speed.

Actually it's normal speed normally but when I record my gameplay it seems to get slower and lag.

Also the wall flashing is annyoing.

Video recording slowing down 0.74 is a known issue.