I'm using Serene Seasons, and I'd like to add rules for mobs to make them more/less numerous during different times of the year. For example, I'd like bears to be more common in the autumn, very rare in winter, and less common during the spring and summer. Can I create a single spawn rule with both spring: True and summer: True, or will that always evaluate to false?

All conditions in a rule have to be true before the rule works. So given that it can't be spring and summer at the same time a rule having both conditions will never work

Gotcha. I figured that was probably the case. I'm guessing, then, the thing to do is have one rule for each season. Thanks!