A Knight or Barbarian hero. Arrangement: Vampire Lords (let's say 18), 1 peasant, 1 peasant, 1 peasant, 1 unupgraded archer. Although it is much better to replace 2 peasant squads with two squads of, for example, pigs from the starting mage hero. Then the red dragon will move BEFORE the Vampire Lords, that is, they will be able to attack from their corner already in the first round. Magic - the ideal option is Bloodlust, because it will last for three rounds, despite the low magic power parameters of the warrior hero.
In this case, we can time the battle so that in the end we are left with the Vampire Lords against the black and green dragons. At the right moment, we defeat the green one and revive 5 units. Then the battle becomes 1 on 1. It seems that 18 Vampire Lords have a chance to emerge from this battle without losses. This is variant 141, as you have probably already guessed. The remaining troops under the control of the necromancer hero went in one direction, and it was only possible to accumulate enough resources for upgrading and buying Vampire Lords by the 4th week, so they took some dragons and opened a second front with the warrior hero (and both the Vampire Lords and the red dragons have the same speed - 5).
If, however, you need to take Dragon City on 131, then it is better to use Alex_R's tactic.

Орден Феникса – харизматический :) лидер