What kind of magic do you like the most?

The description of "hell wave" states that it deals damage to ALL creatures, except demons.

At the initial stage, the hell wave deals 250 damage. This is enough to incinerate any non-summoned creature.

Lava dragons have 280 health, and Arcata dragons have 275, which is more than 250 damage. Therefore, the initial stage of the hell wave is not enough to incinerate any non-summoned creature.

Unfortunately, neutral magic does not grow proportionally to the power of magic, etc. But if you compare spells at the initial level, neutral spells are stronger than regular ones.

Is the initial level level 10 for the hero?

It's just not very accessible.

More precisely, it is only available to 2 heroes, whom you encounter only a couple of times throughout the game.

Added after 12 minutes

And once, I was playing as Necromancer, and the opponent was a mage with Darkness and Sandro's Cloak. It was unpleasant, but not critical. Although, if I hadn't been playing as a Necromancer, who knows what would have happened.

I understand that you leveled up Summoning and won this battle?
If so, then there is nothing surprising, Darkness, even with Sandro's Cloak, is not very effective against a Necromancer. If I were playing Necromancer against Necromancer, I would probably choose Summoning and Chaos/Light.
I haven't played online yet (all my experience playing with other players is playing on one computer), but I hope to test this statement soon.