Hello. It's strange that many people find the last mission difficult. I myself completed it on a difficult level. Initially, I captured a couple of fortresses and simply accumulated resources. At the same time, I cleared out neutral creatures and collected resources with my second hero. I didn't lose troops to neutral creatures, as I usually do since the second mission; after all, magic should be upgraded. I upgraded magic power, plus damage and disabling spells – lightning, chain lightning, explosion, stop time, and mind control. And, of course, I took mass weakening and mass vampirism, which I think everyone takes anyway. I struggled with the third mission much longer.