Played a lot yesterday, three things I noticed:

1) in general the generation of mixed creatures works well, but when fighting any sorts of Golem-type creatures you have to face crazy amounts of other creatures, I don't know if anything in their fight value is calculated wrong but it leads to situations where you need to skip fighting Golems on the adventure map because the mixing is too brutal. Also, Sorcerers and Fire or Water Messengers get generated in absurd amounts. For example 2 or 3 Azure Drakes got converted to 1 Azure Drake and 1600 Sorcerers
I am pretty sure for some creatures there are incorrect values.

2) The setup on neutral monsters is always the same, for example, if you choose "MIX_SPREAD_SPACE_BETWEEN" the creatures will always be setup up in seven stacks and never differently. A little variety would be good, just like in the original Heroes where it can be that there are only two or three stacks in the opponent's lineup. Maybe I'm just using the wrong settings, but can you say something about that?

3) If creatures of the Third Upgrade Mod stand on the adventure map they will always be converted to vanilla creatures. Meaning you do not face any of the creatures you actually attack.
However, if you attack Marksmen there is a good chance that there also will be Crossbowmen (a new upgrade) in the enemy lineup. So this way it works.

These are my observations, thanks