Ah, damn! Physmig writes that if the dwelling is upgraded, there won't be a doubling, as it's the month of the black fly. I'm disappointed:( I won't be able to get to the computer before he builds the upgrade.
The only upgraded unit that can appear in the month of the monster is the hobgoblin. In principle, an unexpected strategy emerges through mass hobgoblins, but that's not quite it:(

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And it's a rather boring sight for streams - generating monsters, catching resistance and morale).