Which race would you add to Heroes?

Firstly, Inferno is already an aggressor.
Secondly, Necropolis NEVER acts openly – their mages will bury everyone in the ground within a day.
Thirdly, Dungeon doesn't have a very smooth relationship among themselves, so they wouldn't unite against everyone else.
And fourthly, these races will never unite – they are too different.
P.S. The author's style is an artistic adaptation of the style of one of the portal's users.

All three of these races are essentially aggressors, not in terms of strength. Or are you saying that Hitler was stronger than Stalin? The weakness in military development relative to the USSR did not prevent the Germans from attacking. This is regarding Dungeon. Secondly, it is stated that an aggressor must act openly. This applies to the undead. And finally, who was talking about uniting these three races?

Added after 29 minutes

A race against which irreconcilable enemies will unite is interesting. But then it turns out that this race must be head and shoulders above all the others. This is an imbalance. Therefore, the race should not be so strong. What else could lead to all uniting against one race? It is a clash of ideas. Outcasts, with the idea of equality and freedom, and Amazons, with the idea of matriarchy, fit here.

AlexeyPank, before your statement, I considered you one of the most reasonable people on this forum, but, as it turns out, your reasoning is not always logical. Remember: there is no race that would force all irreconcilable enemies to unite, all the races that currently exist in Heroes 5!
And even the union of, for example, Inferno and humans is possible only in one case, if the latter sold their souls to Satan, but this is no longer an equal alliance, but a victory for Inferno, which does not correspond to the proposed idea.
Inferno is the aggressor race. And don't spoil your own idea about the Outcasts, AlexeyPank. The Outcasts are good only as neutrals, who for one reason or another can switch to one side or another, to the side of the invaders, or to the side of the defenders.
The Amazons can be aggressors, but again, they will not be able to force all races to unite in order to repel the idea of matriarchy, only because the undead do not care about matriarchy, patriarchy, or anything else in that vein. The same can be said about the soldiers of the Inferno