Leads are another bug in this game that i can't stand at the moment.

yyyyer2Currently in my server I'm making it Christmas themed, therefore I need to add horses but they move A LOT. So how can I make it immobile?

/summon EntityHorse ~0 ~1 ~0 {Attributes:[{Name:generic.movementSpeed,Base:0.0}],PersistenceRequired:1}

/summon EntityHorse spawn a regular horse

~0 ~1 ~0 spawns the horse 1 block above where you're standing

generic.movementSpeed,Base:0.0 Makes it so the horse cannot move

PersistanceRequired:1 is optional in case you want to keep the horse from despawning

Also you could add: ,Invulnerable:1 right before the closing } bracket to make the horse invincible. (You can still kill them in creative mode)

If you use this command to summon it, it won''t even fall.

/summon EntityHorse ~ ~1 ~ {Riding:{id:"ArmorStand",Small:1,Invisible:1,NoBasePlate:1,NoGravity:1}}

Or, you could just get 1 fence, place it down, then get 1 lead, and place it on the horse, and place it on the fence. It will move around a little, but it will stay where you put it, it won't run off.

Summon a horse with NO AI. Search up how to

yyyyer2, hello!
How's it going? Good?
Get the citizens plugin, make npc horses.
http://dev.bukkit.org/bukkit-plugins/citizens/

install the plugin, then add the horse with /npc create Edd --type horse
That's one option at least.