From Wikipedia: https://en.wikipedia.org/wiki/Dandy_(video_game)
Dandy (later Dandy Dungeon) is a dungeon crawl maze game for the Atari 8-bit family published by the Atari Program Exchange in 1983. It was written by John Howard Palevich, originally for his undergraduate thesis while at MIT, drawing inspiration from Dungeons & Dragons, Defender, and arcade maze games. Dandy is one of the first video games with four-player, simultaneous cooperative play. It was the direct inspiration for the popular 1985 Atari Games coin-op, Gauntlet, and later turned into the Dark Chambers home game published by Atari Corporation.
In 1986, Electric Dreams Software, having failed to secure the Gauntlet license acquired the rights to produce the home computer ports of the game. Their intention to release their game as Dauntless led to a dispute with U.S. Gold who were publishing the computer versions of Gauntlet at the same time. Electric Dreams published the game, as Dandy, for the ZX Spectrum, Commodore 64, and Amstrad CPC.
The name Dandy is a play on D&D, the common abbreviation for Dungeons & Dragons.
User Summary of C64/Spectrum version:
This is a game, similar to Gauntlet (1985), in which the player controls one of the playable characters, Thor or Sheba. The game also features a co-op mode, where both can be played simultaneously. The player has to fight his way through 15 dungeons, while collecting treasure. Opponents start in waves from some sort of spawn boxes, which must be taken out as soon as possible to prevent yet another wave.
If all treasure is gathered, a code is granted. At the end of the game, all codes have to be puzzled together.