Seems like CGA to me, rather than Hercules.

Version from the underdogs works just fine under DOSBOX(tm) in glorious EGA graphics and beeper sound.

I have played that version.
Yes, it is cool, but in fact it is NOT PC version.
I have memories on APROMAN King's Valley, so I want to
play it again. UnderDogs administrator says "there is no
PC conversion of MSX King's Valley", but it's not true.
Korean company APROMAN ported the game well, and
many koreans have enjoyed it.
Thanks anyway. 😉

DOSBOX(tm)? Meaning, NTVDM?

No, he, he, was a little joke on myself. With DOSBOX (all caps and just one word, i mean the emulator) as opposite to a dos box (ms-dos box) or NTVDM (NT Virtual DOS Machine). I added the (tm) thingie to DOSBOX name just for fun, heh. 😁 If i would have known it would cause such hassle, i would not had done it. Sorry.

Just a brief update; a forced HGC with the provided zip'd game;
It returns
"!! You must have CGA or EGA or VGA or MCGA."

If I force Tandy (~MCGA), I get this screenshot
(There are still a few modes to implement, I'll try have them
ready for the 0.61 release for ya wiebermensch)

Right, managed to get scrollers working for HGC/CGA/TANDY.

So this game now works.
For those with CVS, head over to
HGC( Hercules Monochrome) WIP report
to update your build.

I will look at adding/fixing EGAVGA scrollers a little later.

I dunno what you're doing to those PNG files, but Internet Explorer 6.0 doesn't like it. 😒

[EDIT] Just confirmed that I could download the PNG and view it in Windows XP's built-in Image Viewer. Internet Explorer 6 doesn't like this image, I dunno why.

Ooh! OOH! I KNOW WHY! IE6 IS SHIT! Yeah, that's right.

Perfect! I upgraded DOSBox 0.60 to 0.61, and then I could play King's Valley! Thanks guys!

You should change dosbox.conf a little.
Change "machine=auto" to "machine=cga".

But the posted image seems more like Hercules monochrome than CGA...

Nah cga 640x200x2 mode

Yes. A CGA video mode very uncommon in games. 😎

If you run King's Valley under VGA, it enters into MODE 04H(i.e, 320*200 4-color graphics).
But if you run King's Valley under Hercules(or edit DOSBox.conf to machine=cga and play the game on DOSBox), it enters into MODE 06H(i.e, 640*200 2-color graphics) and you can play the game without a jerky screen.
Now I shall introduce some programming TIPs. Perhaps DOSBox programmers should already know it, but I hope it should be helpful to newbies like me. 😀
Maybe you should know how to access video memory on MODE 13H(i.e, 320*200 256-color graphics)...if you don't know, you can confer Alex Russell's Dos Game Programming in C for Beginners site.
In MODE 13H, if you want to draw a pixel on (x,y), the only thing you should do is just to put color palette value into A000:offset where offset=y*320+x.
OK. I will return to the subject.
MODE 06H is a little tricky. B800:0000~B800:1F3F represents even lines(i.e, (0,2k)~(639,2k) ), and B800:2000~B800:3F3F represents odd lines(i.e, (0,2k+1)~(639,2k+1) ). B800:1F40~B800:1FFF represents NOTHING!!!
So in MODE 06H if you want to draw 8 pixels on (8x,2y)~(8x+7,2y), the only thing you should do is just to put BYTE into B800:offset where
offset=y*80+x. To draw 8 pixels on (8x,2y+1)~(8x+7,2y+1), put BYTE into B800:offset where
offset=8192+y*80+x.
BYTE is byte representation of 8 pixels. That is, one BYTE consists of 8 bits, and these bits represents black(0)/white(1). MSB(Most Significant Bit) represents leftmost pixel and LSB represents rightmost pixel. For example, 0xA6 represents *_*__**_.

p.s. Next example codes are equivalent:

***** Assembly Language *****
1A28:0100 B80600 MOV AX,0006
1A28:0103 CD10 INT 10 #Enter into MODE 06H
1A28:0105 BF0000 MOV DI,0000
1A28:0108 B800B8 MOV AX,B800
1A28:010B 8EC0 MOV ES,AX
1A28:010D B0A6 MOV AL,A6 #*_*__**_
1A28:010F 26 ES:
1A28:0110 8805 MOV [DI],AL #Put A6 into B800:0000
1A28:0112 CD20 INT 20 #Return to DOS
(You will not be able to see the result because of screen scrolling. If you want to see the result, change last instruction to JMP 0110. You can break infinite loop pressing Ctrl+C.)

***** Turbo C++ 3.0 for DOS *****
#include <dos.h>
int old_mode;
unsigned char far *screen;
void main(void){
union REGS in, out;
// get old video mode
in.h.ah=0x0F;
int86(0x10, &in, &out);
old_mode=out.h.al;
// enter mode 06h
in.h.ah=0;
in.h.al=0x06;
int86(0x10, &in, &out);
screen=(unsigned char far *)MK_FP(0xB800, 0); // screen points to B800:0000
*screen = 0xA6; //*_*__**_
}
(Also, if you want to see the result, append getch();. You should include <conio.h> too.)

***** Quick Basic 3.0 for DOS *****
SCREEN 2
PSET(0,0),1
PSET(1,0),0
PSET(2,0),1
PSET(3,0),0
PSET(4,0),0
PSET(5,0),1
PSET(6,0),1
PSET(7,0),0

or

SCREEN 2
DEF SEG = &HB800
POKE &H0,&HA6 '*_*__**_

Whew, I did it!
I had a lot of difficulties in hacking King's Valley,
and recently I found out why: EXE file was COMPRESSED!!!
I didn't know EXE can be compressed to smaller EXE file!
When I examined the program header,
I found string "PKLITE Copr. 1990-91 PKWARE Inc.",
so I used pklite -x to decompress B.exe
Then hacking it was a piece of cake 😀
I fixed three INT 10 parts to set correct values to registers.
0D13:19BC INT 10(AH=12,BL=10) <- Should set AX FF10 and set CX 000F

0D13:1A7E INT 10(AX=3006) <- Should set AX 3000

0D13:1A23 INT 10(AX=1A00) <- Should set AL 0 and set BX FF10
Now, enjoying the game on real dos or command window is possible.
Enjoy and be happy 😀