Dark Castle Game System is a one or 2 player game and game development system combined into one. Written in Extended BASIC, the game comes with 3 maps (called Strongholds in the game itself, with each of them having the mission to kill an evil king. In 1 player mode, the player (called Adventurer in the game) wanders through the 3D wire-frame dungeon (with scaling as they walk through), killing creatures, getting treasures and objects (and occasionally hints) in a 3 floor castle, with a 5x5 grid per floor.
Where the game is more unique is the 2 player mode (and this runs on the honour system; the two players are each prompted when it is time for them to do something; the other player should turn away or leave the room at that moment). In this mode the the 1st player is the Adventurer as in the 1 player mode, but the 2nd player takes on the role of Castle Lord, which is like a limited scope Dungeon Master from Dungeons and Dragons. Using the existing maps, the Lord will get called upon at random to change things up in the game. This includes moving creatures between rooms (even from different floors), and also any creatures that the Adventurer player havs killed can now be used as Messengers, which the Castle Lord can send to any position in the castle and report back what is there. This way the Lord can figure out if the Adventurer has been there (by them having gotten an object and/or killing a creature in that spot), and adjust where to move creatures to ward the player off before they can reach the Evil King to win the game).
The biggest thing that the Castle Lord can do is create their own maps. There are some restrictions/limitations - all maps must be the same size (3 x 5 x 5), they must contain 20 creatures to start out with (and only 1 King and 1 Dragon per map), and must make sure that there are ladders properly placed so that the Adventurer can navigate between levels. I believe that objects can be placed anywheres (zero or one per location, same as the creatures), and there are also special "Message pillars" (that's what I am calling them; I have never seen the original documentation to see what the author called them) that can give clues to the Adventurer player. Things like treasures, potions, swords, etc. can be of different quantities; there is no fixed amount for them per map.
The Adventurer meanwhile, has the ability to move forward, backward, move left or right (via hallway or door), move up or down (via ladders), and take an object. If a creature is encountered, the player can move towards it (which gives the creature a better chance to surprise the player and render the player unable to fight back for a short period), stay in place and wait for the monster to come to them, or attempt to run away without a fight. The various creature type (including things like giant spiders, skeletons, dragons, the king, etc.) have varying strengths and abilites. Really strong ones can get several attempted hits on the player before the player is can respond with a move of their own.
Like Sir Eggbert Jumper by the same author (who later did Fyr-Draca for Colorquest), the game is a little bit unpolished (there are prompts that don't get bounds checking and can crash out with an error, a few of the graphics get some gaps when scaling, most of the creatures are just called "Creature" rather than unique names (even though the graphics or each creature is unique), and some of the maps don't seem to make sense when looking at the 3d display. On the other hand, it was very ambitious attempting a game that allows both a regular player and a DM style player (and single or 2 player), player created maps, etc. this early on in the Coco's life.
Title: Dark Castle Game System
Author: David Lionell Dawson
Publisher: David Lionell Dawson
Released: May 1982 (1st ad 80 Micro May 1982)
Requires: Color Computer 1,2,3, 16K RAM, Extended BASIC.