- How to defeat Galtran?

Message from ddxdd
No, there's no way... because he's the strongest hero in Heroes 3. I've tried many tactics, castles, and development options against him, but all to no avail (in single-player). How do you stop his skeletons and killing machine? Especially since Galtran almost always gets Air and Earth. What do you think? And what would you advise?

I don't see any particular problem, especially since, as far as I can tell, you're playing as Stronghold. Here's my advice for you:
First of all, skeletons are not the best Tier 1 unit in the game, to put it mildly. Galtran isn't that great of a hero, even though his specialty is skeletons. ;)
Start with the hero Zhbarkas (specialty: Orcs). Let him move at least one unit faster; it will be useful. He also starts with the skills Archery and Offense. It won't be difficult to develop them, and that's how you'll get an army that deals a lot of damage, plus Barbarians always have good Attack. I've always said that quality is better than quantity. You have Tier 2 archers, so use them for their intended purpose. You should also remember to take the following skills: Tactics (essential for Stronghold), Earth and Air Magic (at least Earth Magic), Logistics (always useful, everyone understands that), and Wisdom (a good skill if you get it, which often happens, and from this, you should think about magic skills – try to get Intelligence; if you can't, take Armor).
At the beginning of the battle, if you have Tactics and your enemy doesn't or has a lower level, position your monsters in a way that is advantageous for you, and protect your archers. If the enemy's monsters are all upgraded, then Ghost Dragons will go first (but they don't fly that well). (And you might find a Ring of the Wanderer or a Cloak of Speed on the map; let the birds go first. Also, pay attention to the terrain you're attacking on; it's better to attack on your own territory).
Don't let the birds get ahead; wait, and remember that you have archers.
Shoot the skeletons, then you can sacrifice some Goblins; you should have enough of them. After the enemy's attack, send in the Riders; the skeletons won't be able to handle it, and of course, you have your super weapon, Ancient Behemoths; there won't be anything left of the skeletons (you can cast Bloodlust on the Behemoths or the birds). If the skeletons are still standing, finish them off with the birds. But don't forget about the other monsters; try to think through your moves against the enemy. Look in the spellbook more often, and it's better to approach the battle with +3 Morale and +3 Luck, if possible. Well, the map won't leave you without artifacts; choose the best ones.
I don't know what your battle was like and what problems you had with this hero, and I can't tell you how to behave correctly on the battlefield in your situation (I haven't seen it). In any case, I tried to help you; maybe you'll find something useful for yourself.
Good luck! May you have glorious victories! :)