Yes weakness does that same thing too thank goodness. Thanks for your help!
In previous snapshots you weren't even able to hit any entities while having mining fatigue 255, the highest level available for the status effects. When you had a high level of mining fatigue, it lowered the radius of how far players can hit other entities. NOT DAMAGE. Not being able to hit things prevented any sort of knockback. Similar to the friendly fire option you can use in teams, but for only specific players and for a certain amount of time.
Stained glass blocks and stained glass panes also have the same issue as the slimeblock
Yeah, it is. Is it the fact that it's a custom spawner that makes mobs spawn in walls?
Really? So blocks directly overhead not suffocating them makes complete sense, right? And blocks that don't even seem to touch the horse suffocating it does?
Another comparison of what doesn't and does kill the horse.
Seed is 734378811496951047, coordinates of structure are -1148, 8060