Heroes 5.5 WarGame Edition - Tactical Edition.

The problem is that dragons aren't made of stone. At best, you can give earth immunity to emerald dragons.
Otherwise, the question arises of giving all dark dragons immunity to Darkness (which, of course, doesn't exist in the game) :)

Immunity to darkness should not be compared to immunity to earth, because in Heroes 5, we don't have an "earth magic" school, but we do have a "dark magic" school. We don't have full-fledged earth magic; we just have 4 spells related to the earth element (Shock, Meteor Shower, Stone Spikes, Plague).
That is, in this case, the concepts of "immunity to earth magic" and "immunity to dark magic" cannot stand side by side. Let's consider dark magic and its distinctive features: - in addition to the fact that it is a school of debuffs, we can identify another distinctive feature - all mind magic spells are in darkness, and here is an ability that gives immunity to several spells - this is the ability "immunity to mind magic," and it is the one that can stand next to immunity to earth - in both cases, we have abilities that give immunity to several characteristic spells of a certain element; therefore, I suggest giving Light Elf dragons immunity to earth magic, and Dark Elf dragons immunity to mind magic

Added 1 hour 14 minutes later
by the way, what about the neutrals - how many are there, what are they like, will those two unused IDs be used (Yeti and Black Knight)?