Heroes 5.5 WarGame Edition - Tactical Edition.

P.S. There's an option to tie such a powerful Necropolis building in your mod, like the Temple of the Underworld (where capturing villages transforms their creatures into undead), to a less popular base (branch) like zombies or ghosts (for example), thereby increasing the appeal of this tier. Linking the Temple to the Stronghold makes this branch more of a priority (for days 4-7 of the first week) than others.

That's exactly the point: if you consider the conditional value of the Temple to be 0 (no transformations), then the early-game starts with Castle or Reaper are relatively weak, but if it's not 0, then it's a different story. But how to specifically assess the benefit of this building in the early game is still unclear. It's like a kind of analog to training grounds, but without a limit and with conditions (bring in enemy creatures, i.e., high-tier units must be built in the Necropolis and in another city, because there's little benefit at low tiers).