I'll keep it short and sweet. I beat MM1 about a week ago and could finally polish all quest bugs. That said, I'd like to provide you with the final version of MM1 using ScummVM and it's enhanced interface. I can confidently say it was a real pleasure playing the enhanced version.
Get it HERE. The folder contains: changelog, patch code (if anyone's interested) and the actual fixed game as .zip.

Sidenote: I'm trying to port the same concept to MM2. The fact that there's a reverse-engineered, rewritten MM2 engine already publicly available, will make the process much easier. It will take some time though.

NOTEWORTHY FIXES AND ADDITIONS:
- Party XP gain and training now work correctly.
- A blue arrow is shown beside XP value to indicate when a level-up is possible.
- Certain party members are now eligible for multiple attacks per turn, as originally intended.
- Added G/S (Gather/Share) button on character screen, normally available in classic mode.
- Spellbook improved - manual spell sorting with X and scrolling with PgUp/PgDn.
- Quest log implemented - keep track of quests with K.
- Bestiary implemented - unlock enemy units and their stats through encounters and check with N or click the black skull icon in the interface corner.
- Post-combat loot (sacks, boxes and chests) are now finally enabled, as intended. Previously, only gold and gems were received (yeah, sucks).
- Many game-breaking quest bugs corrected.
- Spell behaviour corrected.

A QUICK GUIDE TO GET STARTED

***Need to have MM1 and MM4/5 already installed.***
***Don't forget to copy "xeen.cc" from MM4/5 to your MM1 folder, it's requiered for the UI.***

- Just unzip the fix (it's portable) .Run the .cmd file. Point ScummVM to your MM1 folder and play.
If you had already been playing, just overwrite existing files.

- Do not run scummvm.exe or it might trigger your previous settings. Please check README for detailed setup.

- You can bring your previous saves into the fixed version. Classic saves should work too, just rename them to the enhanced format (add "_enh" suffix to the filename).

- Don't forget to save often. Saving/loading takes only a moment: press CTRL+F5 to invoke ScummVM menu, then SAVE/LOAD. I suggest remapping CTRL+F5 to TAB, it's quicker.

IMPORTANT: scummvm.exe is a newly compiled, unsigned custom executable. Some antivirus programs may treat an unfamiliar custom build as suspicious or false positive. The final version of the game will be available ONLY here via the Google Drive link above.

For continuity sake, older posts about the topic are here and here.

Apropos of my earlier post - I've squashed all the bugs I had encountered (a legion😄) and finalized the fixed build. It *should* work smoothly for everyone. If interested, feel free to try it out here.

-- NOTE 4/9/26: I've found 4 more minor bugs... will put out an update in a couple of days
fyi: combat party exchanges, prisoner issues, detect magic/trap not responding, gem farming bug

The game was officially rated as "Good" in terms of stability, a rather generous assessment. I'd personally rank it as poor at best. As I keep playing, I come across new bugs, mostly related to quest logic. Just last night I wasn't able to finish Lord Hacker's quest as its handler was tied to an entirely different quest. So anyone playing it would get permanently stuck in his throne room (unless you kept a recent save).

That said, I can't guarantee the game is 100% fixed as I'd need to finish it and complete all the quests first. I'll keep the link updated if any new fixes are applied in the future.

WHAT WAS TESTED?
The fixes were checked through source review and play testing. Tests included spell targeting and cancellation, spell damage, combat messages, monster attacks, backward movement, loading from location screens, Temple services, Quick Reference text and combat-screen drawing.

Quick notes to get started:

***Need to have MM1 and MM4/5 already installed.***
***Don't forget to copy "xeen.cc" from MM4/5 to your MM1 folder, it's requiered for the UI.***

- Just unzip the fix (it's portable).

- Run the .cmd file. Do not run scummvm.exe or it might trigger your previous settings. Please check README for detailed setup.

- You can bring your previous saves into the fixed version. Classic saves should work too, just rename them to the enhanced format (add "_enh" suffix to the filename).

- Don't forget to save often. Saving/loading takes only a moment: press CTRL+F5 to invoke ScummVM menu, then SAVE/LOAD. I suggest remapping CTRL+F5 to TAB, it's quicker.

IMPORTANT:

- scummvm.exe is a newly compiled, unsigned custom executable. Some antivirus programs may treat an unfamiliar custom build as suspicious or false positive. Take precautions if concerned (check file source, my link above is the only valid one; compare checksum).

Consult CHANGELOG and README included in the archive for more info.

I'll get straight to it. I've been a fan of the franchise, but just recently decided to tackle the old school MMs.

I got MM1 on GOG, but decided to import it into ScummVM for that extra quality of life (maps, save game, MM4 UI). Supposedly, MM1 got supported in 2023 and ranked as "good" regarding compatibility and issues. Yeah, IF ONLY...

It's so bug infested that it's game-breaking. I spent my whole yesterday debugging and compiling and finally I might have just polished it to the point where I don't need to look back anymore.

So has anyone played it with ScummVM? Curious if anyone had issues with the game.
I'll be happy to share the adjusted version, just ping me if you wanna try the glow-up.

changelog fyi:

Combat and encounters

• Fixed encounter monster-tier selection so harder regions can generate the appropriate enemy groups.
• Improved the debugger encounter command and its enemy-count validation.
• Fixed single-target spell bookkeeping/counters.
• Fixed monsters killed by spells remaining in combat as usable “corpse” entries.
• Fixed party corruption caused by the rear-rank shooting fallback copying one complete character record over another.
• Fixed monster-spell crashes caused by using the encounter-list index on _remainingMonsters.
  • Corrected Fire, Paralyze, Explode, Fireball, Fire Breath, Poison, Lightning, Frost, Spikes, Acid, Fire and Energy spell handlers.
• Fixed enhanced monster-spell messages sometimes displaying a blank interval instead of the spell and its result.
• Fixed the monster Paralyze spell applying/reporting the wrong condition.
• Fixed Paralyze displaying “is slept” instead of “is paralyzed.”
• Added diagnostic combat-mode tracing used to distinguish attacks, spells, waits and infiltration actions.

Spellcasting and spellbook

• Fixed enhanced-mode spell-point and gem-cost handling.
• Fixed the Spray Acid localization/string crash.
• Fixed Turn Undead timing/assertion problems.
• Fixed the spellbook learned-spell count being off by one.
• Added a custom practical spellbook order:
  • Cleric list prioritizes healing, buffs and commonly used combat spells.
  • Sorcerer list prioritizes buffs, control and frequently used attack spells.
  • Paladins inherit the Cleric order.
  • Archers inherit the Sorcerer order.
• Preserved the real internal spell numbers when displaying and selecting reordered spells.
• Fixed spell progression class checks:
  • Cleric and Sorcerer gain spell levels at character levels 3, 5, 7, 9, 11 and 13.
  • Paladin and Archer gain spell levels at levels 7, 9, 11 and 13.
• Fixed level-up code calculating a new spell level but never assigning it to the character.
• Recalculates spell points when a newly earned spell level is assigned.

Interface and messages

• Fixed enhanced monster-spell rendering of lines with default (-1, -1) coordinates.
• Fixed Quick Reference condition text overflowing into adjacent character rows.
• Quick Reference conditions are restricted to five characters on one row.
• Fixed replacement of an active enhanced GameView location animation, preventing the _anim assertion crash.
• Fixed several combat messages retaining or failing to replace older text.

Movement and map interaction

• Fixed backward movement incorrectly behaving as though every rear direction contained a wall.
• Consolidated backward movement with normal movement collision and map-transition handling.
• Preserved direction-dependent special-tile behaviour: entering a special tile backward does not automatically trigger an interaction that requires facing its activation direction.
• Added load-time handling intended to stop a restored position from being processed as a newly entered special tile.

The special-tile loading issue is not fully resolved: loading a save associated with the trainer/temple tile has still reopened or left the location interface in an incomplete state during testing.

Locations

• Fixed multiple training-related state and interface problems.
• Fixed Temple character switching so another party member can be selected without leaving and re-entering.
• Temple service costs and available options are recalculated when switching characters.
• Temple options are refreshed after healing, removing curses or restoring alignment.
• Fixed Restore Alignment remaining visible after the selected character had already been realigned.

Travel

• Fixed the Fly destination selector so outdoor column E can be selected.

Still under observation

• Occasional combat actions apparently causing damage without a complete visible attack/spell message.
• Failed monster spellcasting only reports that the cast failed, without identifying the attempted spell.
• Loading while a trainer/temple interaction is active or associated with the saved tile.
• WASAPI initialization failure is environmental/audio related and not yet part of the engine patch set.