Doki Doki Penguin Land & Doki Doki Penguin Land Uchū Dai Bōken need to be split:

Doki Doki Penguin Land (どきどきペンギンランド) is a port of the arcade machine. This would include the Gameboy & MSX releases, and the SG-1000 release not yet in the database. Pretty much all the ports/variations that start out in-game on a snow covered landscape with an igloo in the background.

Doki Doki Penguin Land Great Cosmic Adventure? (Doki Doki Penguin Land Uchū Dai Bōken / どきどきペンギンランド 宇宙大冒険) is a sequel that takes place on another planet. This would include the Master System 'Penguin Land" / Mark III "どきどきペンギンランド 宇宙大冒険" (not yet in the database). Pretty much all variations that start out in-game on a crater covered planet/moon landscape with a spaceship in the background.

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EDIT: I'll be adding a separate entry for the SG-1000 card so I'll request that the Gameboy & MSX version screen shots be moved, and that the alternate title data be corrected as well.

If you look at the correction that has been pending for this game entry (Contribute - Corrections - Pending Corrections) it states that the MSX version is probably an unofficial hack of the SG-1000. Can you confirm that? If so, MSX should probably be removed altogether.

Also, Wikipedia says the SG-1000 game has a "loose adaptation" on the Game Boy. So GB possibly also needs an entry of its own?

Gameboy version looks like a straight up conversion to me (same level layout), it just uses side scrolling because it is unable to show the entire width of the play area:

Gameboy:
http://www.youtube.com/watch?v=g__9xraavAQ

SG-1000:
http://www.youtube.com/watch?v=SUxLthm9u_I

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The MSX version looks like a Ponyca port and/or manufacturer/distribution to me (found images of 2 different cartridges with different print on the front though):

Variant a:
http://i45.tinypic.com/9iwglh.jpg
http://auctions.c.yimg.jp/img307.auctions.yahoo.co.jp/users/9/9/9/8/potetolife1-img600x450-1263901514ypogbd42690.jpg

Variant b:
http://auctions.c.yimg.jp/img333.auctions.yahoo.co.jp/users/8/1/4/8/taike2-img600x450-1317043462rvray815433.jpg
http://auctions.c.yimg.jp/img333.auctions.yahoo.co.jp/users/8/1/4/8/taike2-img600x450-1317043462wweion15433.jpg

Anyone know what the extra text on 'Variant b' says? (looks like it was covered up by a sticker which was later removed...)

The two lines say 見本品 (sample item) and and 非売品 (not for sale).

OK, so that one is simply a display model / promotional copy. Thanks!

Note that Pony, Inc. (Ponyca) also handled the manufacturing and distribution of the MSX port of SEGA's Ninja Princess the next year as well:

http://img87.imageshack.us/img87/6696/img210517130516801.jpg

http://blog.goo.ne.jp/80-cafe/e/9bd19158c5eb31334453ed24225a926c

The MSX versions of both of these SEGA games look rather legit to me.

EDIT: This is best quality box art that I could find floating around the internet for the MSX version (note the Ponyca logo in the top right corner):

http://segaretro.org/images/0/06/DDPL_MSX_JP_Box_Front.jpg