Clearly state the problem. For example, Warrior, Tears. 4th month, army is like this, upgrades are like this. Attacks, enemy hero - has and leaves.
I completed this mission with a Blood Mage. The only problems were with the crystals; I closed all the portals.
I had no problems with the computer! Tactics: 1st turn - summon Fire Elementals, 2nd turn - general Resurrection - if the opponent is a mage and attacks in an area, but if he's a warrior, then Resurrection on one of my units that he's attacking. Cyclops under the mage - with a beam, they burn everything that moves.
I don't know where your problem is. I always play on "Hard".
The Demonic Worm is not a problem at all!! Moreover, I earned the "Caesarean Section" achievement on it. I even waited a few turns for it to swallow someone)))
So, Sensi and Faj - who are you playing as? Mage/Warrior? Tears/Blood?