This topic doesn't seem to be one that has ever clearly been answered. I've been looking on the forums for hours and I can't find a solution -- how do you enable either cheats or the debug mode for HOMM2? It's one of those cases where a limited few of the codes work...and most don't. The debug mode seems to be absolutely impossible to get working. Can we get this resolved once and for all?

The Debug Mode doesn't work in the DOS version of the game. But GOG offers optional the Windows version as bonus content. There you could add " /nwc" to the executable in the game's shortcut to activate it (right-click => Properties). While in-game, press F4 to access windowed mode and you should see a debug menu (not available at menu screens).

The numerical codes work also in the DOS version. Type the codes directly on the world map while playing a scenario:

In The Price of Loyalty:
32167 => 5 Black Dragons (select your hero before entering the code)
844690 => Additional Crystal
899101 => Additional Gems
101111 => Additional Gold
844691 => Additional Ore
8675309 => Display Entire Map
101495 => Instant Exploring
1911 => Last Level
1313 => Loose Scenario
911 => Win Scenario

In The Succession Wars at least these should work:
32167 => 5 Black Dragons (select your hero before entering the code)
8675309 => Display Entire Map
101495 => Instant Exploring
1911 => Last Level
1313 => Loose Scenario
911 => Win Scenario