Even a two-week newbie can easily defeat you with that build. And someone is still trying to teach great Necromancers.

Outcasts are just average.

There are plenty of neutral creatures.

Read the material and don't embarrass yourself. Mages have a large part of their army protected from Chaos, one way or another.

Read the above, I wrote that the Mage is protected.
Outcasts is a very small map (not in size, but specifically as a map, the game on it lasts one and a half to two weeks). The last time I played Heroes was in 2008, and Outcasts were popular then. A Chaos build could defeat the Mage due to the element of surprise. But the main advantage here is that such a rush build defeats everything! Gremlins and Mages are destroyed immediately. The opponent won't even have time to get Titans.
This venture at least gives a chance to defeat him.

Added 5 minutes ago

I just haven't encountered such a fast opponent. That's why I asked for help from knowledgeable people. After all, a quick start is 70-80% of the key to victory. And when they take away your Utopia right under your nose (and that's a big bonus to money, artifacts + top spells in the first week), and on top of that, you yourself run away with a significantly reduced army - that's not good.

Sometimes, against a strong opponent, you can only win by playing in an unconventional way and surprising him.
But Outcasts is very standard. You need to defeat the opponent only with a rush (leave the Castle in the direction of his Castle and win). In the late game, you can no longer defeat the Mage with a Necromancer. Only a rush and trying any build for a rush.

Added 4 minutes ago

In general, he's a strange guy. Either he's a real genius, or he's a cheater. At least, how he gets the Utopia is a mystery to me. There is, of course, a building that provides regeneration, but it doesn't always appear. And the Crystal too. Suspicious.

There is AI behavior where the computer can focus on single units, even if there are other available troops to eliminate them at the moment. The Crystal and Wall are too overpowered against the AI. A building that provides regeneration is deadly for magic races. And Vampires with a building that provides regeneration also easily take the Utopia. There is also Deadly Cold, Golemageddon, and just - Yellow + Chaos. There are many cheesy loopholes, but everyone can use them. The same Secret of the Phoenix can be very strong.

Added 53 seconds ago
The opponent is definitely using a scanner.