Blue crystal

I hope the second attempt will be successful.)

The map is evil... 7 months and 3 weeks ago, I reached the last guardians, and I won the earth, air, and water battles on the first try without reloading... but the fire guardian is overpowered; I've been struggling with it for an hour, trying to level up with the mentor, replaying battles, trying to come up with something, but it's all in vain...

In my army, I have 2.5k skeletons and 100 archliches (I'm fighting with a limited army); fighting with a full army is not an option against any of the guardians, especially the mages...

How did you win it? Those who have completed the map, please tell me in more detail...
I put all possible artifacts on fire and lightning resistance, boots for 10% resistance, I used a light artifact for +50% fire protection, and in the sorcerer branch, I took +20% chaos protection; in total, the fire resistance with artifacts is 150%+, but he doesn't even flinch; he knocks me out with a fireball across the entire front line and deals at least 5000 damage with Earth Shock per cast.

I also use a scroll of antimagic with an artifact of light, and I put antimagic on the skeleton... and he casts Earth Shock on me; how is that possible?
Level-up #1, #2, and the fire boss himself are in the attachments.