I have seen a few people in need of a simple, light weight plugin that allows them to stop mobs from moving.
NoAI allows you to specify which mobs aren't able to move, as well as from what spawn methods.
This is great for turning off AI for spawner mobs so that players grinders work better, and also goes great with my MobStacker plugin. (Mobs must have CUSTOM spawn method listed as disabled for MobStacker to work properly with this)
NOTE: This uses NMS, so is very version specific. 1.8.3 and up should work, but nothing below will.Code (YAML):
# To add more mobs, follow the layout below.
# All spawn reasons: https://hub.spigotmc.org/javadocs/spigot/org/bukkit/event/entity/CreatureSpawnEvent.SpawnReason.html
# All mobs can be found here: https://hub.spigotmc.org/javadocs/spigot/org/bukkit/entity/EntityType.html