Oops, my bad, that is only used for flying mobs it turns out. Specifically used for flying. It turns out you might have to subscribe to PlayerEvent.StartTracking and "tag" the entity and "untag" the entity in PlayerEvent.StopTracking. And then in a tick event check if they have the potion effect and send the packet and mark that so you don't continuously send the packet. And then check if they don't have the effect and send another packet letting the client know. Honestly, you might even want to skip the Tracking section because it might work better.