OoE works flawlessly on all cards I think. PoR has freezing problems on most retail flashcarts. DoS randomly froze on me about 3 times (R4). Maybe you've got a bad dump?

 

I suppose it was a bad dump, got a different one (US instead of E) and it works fine, played through Wizardry Lab with no problems. Athough.....

This kind of surprises me, especially the "any" Castlevania part, unless you've never played Portrait of Ruin. PoR was pretty well known for its freezes although I was still dismayed to find out that my new slot-1 solution didn't fix it like I was led to believe it would

Anyways thanks y'all for the responses.

 

I went through all of Portrait of Ruin without ever experiencing a freeze on my Real. A high-speed card (Class-4 or higher) is fast enough to overcome problems with games known to freeze in this way.

 

When I encounter the Puppet Master-boss (the one which gives you the soul that lets you toss puppets and switch places with it) the music is gone, and when I beat it end exit the room the games freezes. The game also freezes if I die on the boss. So apparently, since the music is gone when I encounter him, the glitch/bug/error is present. Is there a way to circumvent this issue?

EDIT:
Tried a bunch of different firmwares, all of them gave me the same issue.
So I copied my .sav and loaded it up in No$GBA, beat the boss, saved. I then converted the save at: http://www.shunyweb.info/convert.php
Changed the newly generated extension .0 into .sav, copied it back onto the SDHC-card and loaded the game as usual in Sakura. Worked like a charm. Quite a process, but atleast I'll be able to continue.. that is, until I (hopefully not) hit another freeze somewhere.