So the problem I'm having with the dragon is, she respawns, but up at like 255, and she is stuck there, doesn't move.

Is this a problem other servers are having?

Server version, plugin version? /version extrahardmode

server version: CraftBukkit version git-Spigot-596221b-2c5c611 (MC: 1.12) (Implementing API version 1.12-R0.1-SNAPSHOT)

Plugin version: ExtraHardMode version 3.12.1

EntityHelper.spawn(new Location(world, 0, world.getMaxHeight() - 1, 0), EntityType.ENDER_DRAGON);

I'm guessing you have a block at 0, 254, 0...? But that wouldn't explain the dragon getting stuck... Wondering if the AI might be confused due to the new enderdragon fight sequence (since 1.9 iirc)?

Oh man that was so long ago. But Im PRETTY sure there wouldn't have been a block there.
Dealing with some stuff in the Skript community I have come to find out the Dragon AI situation is messed since I believe like you said 1.9. Even if you use the Minecraft /summon command, it'll summon a dragon without AI.
Maybe this is something that cant be fixed?

Im just looking at the Wiki now, and I came across this

Commands[edit | edit source]
The /summon ender_dragon command, by default, summons a harmless ender dragon that hovers
 in place. Setting the DragonPhase tag (for instance by issuing /summon ender_dragon ~ ~ ~ 
{DragonPhase:0}) will create a normal ender dragon, but it will have no health bar since the bar
 is managed by the End's dragon fight status rather than by the dragon entity itself. If spawned
 away from the center of the map (X:0, Z:0), the dragon will first fly to the center before 
resuming normal behavior (see #Behavior).

Not sure if this helps you any.

Likely the cause: https://korobi.io/network/spigot/channel/paper/logs/2018/11/13/#L835

Ah... well mystery solved for why it didnt work. Damn him. Hopefully they can PR and fix that