I have created an actually useable biome in the April Fools infinity snapshot. A Nether with ice lakes & pyramids. Unfortunately it also has 64 very noisy Ender Dragons who sometimes blow my stuff up when they get tired of chasing their tales. (If you want to play this world, use the phrase "circus freak" when it asks for text).
I have already destroyed the end crystals.
I tried playing in Peaceful, but they still spawn.
I tried /gamerule doMobSpawnign false but they still spawn.
In reality, I actually do want mobs to spawn, just not Ender Dragons. Especially not 64 of them.
I have tried /kill @e[type=ender_dragon] which is how I know there were 64, but they respawn minutes latter.
Is there anything I can do to prevent them from spawning?