Magnus
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my squad: Monk, Thief, Priest, Archmage
I really don't understand how you can play M&M without a Thief. How did you open chests?
And I didn't let them. Before entering, I buffed the party with a full set of light spells and activated invisibility. Then, I ran up close, and the Orcs have thin skin, so they're easy to defeat. Moreover, the Archmage acted as a warrior. With a full set of light blessings, he's an incredibly powerful unit. Of course, you can run through the corridors and throw stones, especially for a party of 3 wizards. They tear everything apart, even better than dark magic.
This is a playstyle I developed starting with Heroes 6. Since I already remembered the interval between recovery after using the "Jump" spell, it's very easy to use. Everything is done in real time. Jump to the Necromancer, and the rest of the party unleashes a barrage of attacks, then jump back or to the next target. Vampires and other undead are so weak that I didn't waste spells on them. Running across lava is restored with regeneration. I practiced this method in the Minotaur Labyrinth and the tunnels of Nighon.