Luke Heidbrink

Encountered the same issue. I can't get slowness to work with /summon. I can tell I have the syntax right, because on the same mob I've got Resistance 5, making it invincible, and that's working fine. But slowness and speed don't seem to have any effect.

/summon Skeleton ~-2 ~1 ~ {CustomName:"Skelly Tim", CustomNameVisible:1, Equipment:[{id: 340,tag:{ench:[{id:16,lvl:-5}]}}], ActiveEffects:[{Id:2,Amplifier:5,Duration:9999999},{Id:11,Amplifier:5,Duration:9999999}]}