Let's come up with something instead of a swamp.

And here's another idea: I think it would be better to give "training" to the Lizardmen, and give "blood rage" to the Humans – just rename it, and let it give points for defense?

On level 7, we can add Wendigo to the Chimera Mages.

for example, Humans will have angels and dragons – but won't it turn out that in the creature upgrade window, we can turn an angel into a dragon and vice versa (like we do with the regular and alternate upgrade of creatures) – this is clearly bad.
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Maybe if we don't make the angel a "pair" for the dragon, but just place them in the same building, there won't be any problems? The simplest solution is to make the cost for retraining to level 7 a huge amount of resources and gold.