Okey, some things to correct here, as I noticed that during playing the game (and I used to play it maaany times
).
Life-Leeching
1. First of all, if a unit or a hero has a life-leeching ability (artifact, skill), the increased chance to hit REDUCES the chance to leech the life (thus also reducing the chance of killing an enemy completely with life-leech). Therefore are the Deathknights and heroes not so good to have this ability - little use of it then, as they have good chance to hit. And the better the chance to hit is, the less the possibility to leech life.
2. Second, the ranged attacks DON'T leech life. No, they don't. I tested that many times, especially on Ravashak when he still was weak and had little chances to hit. Didn't work. Also doesn't work with the Demonlord. (This is a bug)
3. Third, ANY unit can be raised from dead through life-leeching. I was able to have a colossus killed with the wraiths once, and I had him after as an undead unit. But, a summoned unit turned to undead state costs additionally 0.5% of mana to their normal mana cost. Thus useless on summoned units, they're better as non-undead then. Also it works on heroes. Oh yes. Got to love this unique Lifepriestess hero when she passed away with help of the wraiths early in the game.
But the during the combat summoned units can't be raised from death after the combat ends. No way. Tried that with Air Elementals and Earth Elementals. Enemy can have them, but players not (this is a bug).
Invisible Units / unexplored terrain
1. Any invisible unit CAN be seen by computer enemy. You have to think, the computer enemy is the computer that runs the game, and as such he knows and sees everything in the game. Yes, the computer enemy players should behave as if they wouldn't see the invisible units, but they don't in this game. They can see and attack invisible units on the map, just that they "can't see" them in combat (at least that works).
2. Also, the enemy computer players don't need the map / player revealing spells (Nature's Awareness, Awareness, Earth's Lore) as such, they can see every player and every place on the map at once. Just think on Jafar, when he casts his Floating Island near your starting city, should be known to everybody, is a common event. He doesn't have any units near your city, neither does he have any terrain-revealing spells cast. So this is also the awareness-cheating of the computer.
Heroes with chance to hit
Some heroes have that skill that increases their chance to hit (forgot the name) additionally. Now, if you create an artifact for them that has the maximum possible bonus value to hit on it and the hero has this chance-to-hit increasing skill AND the hero has a high level like Demigod AND the hero is a melee attacker only - they very often won't hit the enemy anymore. This seems to be also a bug of the game, in that with this combination the chance to hit of a hero goes over into a negative value because of the too high number. How to negate it? Don't add the chance to hit bonus to an artifact for this hero. Should be fine then (was then for me).
With that said, there are many more bugs in the game, like the game crash on casting the Chaos Channels Lycantropy spells sometimes. Or also that the volcanoes converted to mountains and further by the Change Terrain or that very rare Nature global spell spell stop to produce mana. A pity there was no additional patch for that, but this is how the game will remain now seemingly forever...