The “Island for One” scenario.

To successfully complete the game, it is enough to level up one hero to level 30, have 60 dragons, 400 vampires, 150 liches, and 150 undead. Such power will defeat all four orange players, all their thousands of mages, rakshasas, and hundreds of giants!

Added after 14 hours and 22 minutes
Although, if you are playing as a hero, there is simply no escape from the enemy! He keeps coming and coming, the bastard! And most importantly, he can see the entire map! As soon as you go out to sea, he immediately flies in, attacks, and even whirlpools don't affect him! Therefore, you need to sail to the revealed Grail with a secondary hero. He will also pick up a chest with experience there and gain some skill in a hut. Then, after dividing your troops, you need to attack the green or earth elementals, flee the battlefield, and reappear in your castle! Done, the Grail is yours, and you are ready to fight a strong opponent. The main thing is to exhaust him; it will be difficult at first, but you need to accumulate strength. Fortunately, on a difficult level, he doesn't run away, so his major heroes will gradually be eliminated, while yours will become stronger!