FriendlyFire-1.12.2-1.5.9
BabyMobs-1.12-1.5.5
Forge 14.23.5.2807

The BabyMobs version of the Cat that follows around the Minecraft Witch [not the Ender Zoo Cat] has the label "tamed" and you cannot attack it [not sure if the label matters but so far the only mob I have found that has a issue]. One of my players thought it was a joke until it got serious; He died.

Will be sharing this with BabyMobs as well.

Thanks for reporting this issue, and sorry for the long delayed response. You can circumvent the protections provided by this mod by sneaking. In 1.13.2+ I will also be adding additional checks to prevent these situations.