Ender Dragons Keep Spawning?

Hey -- so in my minecraft world, my friend thought it would be funny to spawn a bunch of enderdragons, and when i joined the server I would be in for a surprise. Well, I saw a bunch of dragons and did the /killall and /butcher command. They all disappeared, which is good. But whenever I save the world and join back, the dragons aren't there but they start respawning. And there are like 100's of them, and I don't know what to do. I worked hard on the server.

Kill your friend XD

Sounds like an Ender Dragon spawner is at work, especially if they are continuously spawning as you say they are. Keep an eye out for where they're spawning -- needless to say, entities spawned by mob spawners generally appear from the same location. FInd the spawner and you'll be able to stop the dragons from appearing.

If it's any help, disable mob griefing if they're spawning in the overworld (/gamerule mobGriefing false) to prevent them from destroying your server until you've located the spawner.