How is melee combat actually resolved in Xeen (or Terra)? If I have a level x Knight with an accuracy bonus of +y attacking a monster with armor class z, what is my chance to hit? If I have n attacks per round, do all of them get rolled seperately or does it just work as a damage multiplier? Any and all information would be appreciated.

The attacks are added together before the enemy AC comes into play so for a character with only 1-2 attacks per round it might be impossible to damage a monster while a character with twice as many attacks per round might kill it quickly.

The Xeen Slayer Sword is that special weapon I mentioned in my first post. It is very useful for that reason. In addition, it is unbreakable: even being eradicated won't break the sword (and you can then trade the sword to someone who can still fight). (It's also worth noting the cheat that allows you to get extras if you don't want to deal with constantly trading it.)

The thing with AC is that, in the later stages of the game:
If your AC is low, raising it won't provide any benefit unless it gets close to the enemy's AC.
If your AC is high, the enemy's chance of hitting is at its minimum, so raising it further will provide no further benefit.
Your AC being in between is unlikely, since there is only about a 20-point window, which is less than what Bless (at high levels) or the Darkside AC fountain can provide.

By the way, if we calculate the damage of the Xeen Slayer Sword used by a level 255 Ninja, the calculation looks like the following:
~20 per hit (remember that we have a Strength bonus to factor in)
+255 for Holy Bonus (cast it from an item)
= 275 per hit
255 / 5 + 1 = 52 hits
275 * 52 = 14300 damage.
64000 / 14300 = 4.47, rounded up to 5 hits to kill the Mega Dragon. This matches the test result on the other forum.

Conclusion: Holy Bonus is way overpowered at high levels. Also, Xeen Slayer Sword's defense ignoring property is far better than Obsidian's damage bonus against enemies with high physical resistance.

On the other hand, Obsidian does have a nice to hit bonus, so if you find yourself on the edge in terms of accuracy, that might help. (Then again, with the help of fountains and Implosions, it isn't that hard to get through the Dragon Tower early and reach level 40+ with access to the +50 level fountain.)

It doesn't seem to work like that at all. MM 3+ formulas aren't as straightforward. Example of MM VI mechanics here. There was a lot of situations in MM 4-5 where I just couldn't land a hit on enemy, hit chance was nowhere near 5% (I played on Warrior).

This page remains unchanged for years now. Looks like I will have to look into code myself to find out how it works... But it will be after I am finally done with few other games out there :)

The ninja was fully buffed and therefore had 113 attacks per round (Level 305 + Level 255 Heroism from Day of Protection).
The Xeen Slayer Sword does 6-24 base damage, strength bonus was +20 for 250+.

This adds up to 113*(281-299) which is 32770 average per round, so less than half the potential damage is dealt.

Actually, your calculation has one mistake. Heroism does not add to the number of attacks, so your Ninja had only 62 attacks, which still yields around 17980 damage per attack.

That figure is still too high, but I can think of one thing that needs testing: Do levels past 255 actually increase the number of attacks the character gets? (How many attacks does the status screen say your Ninja should get? Does your Ninja kill the Mega Dragon any faster at level 305 than level 255 with other weapons?)

Also, remember that at such extreme levels, integer overflows might be possible, which would (typically) lead to far less damage than expected.

I went and pounded on some armadillos (AC 50).

Level 11 Ranger (+11?) 17 Acc (+3) Heroism (+11) Gold Weapon (+4) hit 8 out of 16 times... wouldn't expect him to be able to hit at all if d20+29 had to beat 50.

Level 11 Paladin (+11?) 21 Acc (+5) Heroism (+11) Emerald Weapon (+7) only hit 6 out of 16 times despite better bonuses than the ranger.

Level 11 Barbarian (+11?) 39 Acc (+8) Heroism (+11) Emerald Weapon (+7) hit 16 out of 17 times... too reliable to be d20+37 vs 50.

Level 11 Ninja (+11?) 19 Acc (+4) Heroism (+11) Diamond Weapon (+9) hit 6 out of 8 times (before I missed that one of the Armadillos woke up and didn't Beast Master it back to sleep....)

Is it possible that some factors (accuracy bonus?) get doubled? Or maybe each class has a base to-hit chance... Maybe I should kill more armadillos.

No, it just doesn't operate purely with d20. Accuracy mechanics so far are just assumptions, if someone could look into that Opcode which I linked above, it would be great. I plan to do it myself if noone else wants, but as i wrote, I need to be done with some other games first :)

Heroism does increase the character level in regards to melee combat and therefore the number of attacks although it's not showed in the display. In MM3 there was an overflow if the sum was higher than 255, but not in Xeen (the overflow is only with spells, therefore only level 255 day of protection).

Have you actually tested this? (If so, that makes Day of Protection even more overpowered than I thought.)

Also, since MM3 had an overflow past 255, it is likely that Xeen still uses only 1 byte for this value, and therefore still can't represent values higher than 255. In other words, raising level past 255, whether by the fountain or (if what you're saying is correct) by Heroism will not add extra attacks.

By the way, was the overflow bug fixed in Clouds alone, or was the fix not introduced until Darkside? (Actually testing this will require hacking because Clouds alone provides no means to go past level 33.)

One more prediction: When under the effects of level 255 Heroism (or Day of Protection), a level 1 character should be able to do as much physical damage as a level 255 or 305 character.

How heroism works is described in the WoX manual (Increases temp. level by 1 per caster level), seeing the effects playing revealed that this applies to attacks per round (but not to casting).

It wasn't too difficult getting a character to 255 in WoX, raising it to level 305 with the well showed more attacks per round and the character fought better. But using an item for Day of Protection at level 305 only yielded a +49 bonus.

Unlike MM 3, MM4-5 don't have any overflows, which you can encounter during normal gameplay. Only exception is gold, it will overflow at over 2 billions.