My Swan copied some person's Headless Horseman ability, after first a notification appeared saying that is wasn't able to SUMMON RAIN?

Curious what pet does that...

Anyways, I checked to see, and none of my pets are mutated. They should've just outright make your Swans copy some other pet in another pets garden, like a helpful redirect on the wiki. IF MY SWAN COPIES ONE MORE HORSEMAN'S ABILITY.