However, the opposite practice, where the number of slots is less than the number of creatures that can be built in the castle, would be interesting, as it would motivate players not to build all of them.
Regarding rare and overpowered mobs, "bosses" – this is a niche for tier 7; some players simply play on a map for too long, and tier 7 ceases to be something special, the pinnacle of development, which it should be.
Well, in general, we are getting a bit off-topic here, as the topic is about a collection of existing mods, not about fantasies about creating new mods.