The main reference information has been posted on the website.

Added 20 hours and 8 minutes ago
It was decided to reintroduce re-upgrades on the map (previously, only a single "upgrade" from the base version was possible).
The following question was raised:
1) either hire upgrades at a 20% discount
2) or give them the same rights as the base units (i.e., give them the same flexibility)

The second option seemed better.

I wanted to set the price of a re-upgrade to 20%, but it wasn't technically possible, as the game performs the re-upgrade using the upgrade mechanism (choosing 1 out of 2).
Therefore, the re-upgrade will be free.

However, given the ban on chains, the main limitation is the fact that the troops for re-upgrade must be in the city. So, it won't be possible to abuse it.

Also, the hiring prices of creatures will be adjusted in accordance with what is stated on the website (a 1.5 times reduction).
The top-tier creatures will cost:
1) light and dark dragons: 3000 + 2 rare resources (crystals and sulfur, respectively)
2) titans, cyclops, devils, dragon riders: 3500 + 1 rare resource (gems, crystals, mercury, sulfur, respectively)
3) rakshasas, hydras: 4000
4) phoenix: 2000 + 1/1/1/1 (gems + crystals + mercury + sulfur)
5) angels, necrodragons: 1500 + 1 rare resource (gems and mercury, respectively)

In general, the prices of tiers 4-7 will be similar to the original Heroes 5 (upgrades). And the prices of tiers 1-3 will be similar to Heroes 3 (in the Fifth part, low-level units were too cheap).

The cheapest unit – the peasant – will cost 40 gold.

Added 7 hours and 13 minutes ago
Regarding abilities.

Ice dragons will lose their immunity to fire, which will be given to Jarls. Previously, immunity to fire was technically necessary (due to a shortage of technical abilities), but now I have found a way to bypass this limitation.

Therefore, the immunities for dwarves will be as follows:
- to fire: fire dragons, lava dragons, and jarls
- to air: erls
- to water: ice dragons