Oh man, can't believe you found it, Mail Order Monsters. We spent so many hours playing that game, building up our characters so high, until the disk with the saved characters stopped working. I think I used some amoeba guy, but I can't see the back cover very clearly to look at the characters.

And now that I look at the pictures for Racing Destruction Set, I see that we had that game as well, and so can understand your confusion. I'm not sure if we had Adventure Construction Set, but I know we had a similar game where you could build a board, and fighting enemies consisted of hits and misses based on semi-random numbers. I think it may have been called Boulderdash... nah, that was a different game. This one had green snakes and trees, and lambs, maybe keys... dang, what was that...

Hrm, no luck finding the Atari 8-bit roms, but C-64 versions are available on Arnold. If yer getting C-64 roms, make sure you grab a copy of Wasteland, a great game that never made it(why?) to the Atari.

Yeah, ACS was Commodore only, far as I know. The game yer thinking about was something that came out of Antic Magazine. I forget what it was called, but was basically the same concept.