you tried to make the EnderDragon attack players but I looked in the NBT TAG and found this:{Motion:[0:NaNd,1:NaNd,2:NaNd]}
MC-102204
EnderDragon NBT Tag bug.
Resolved
Invalid
0
(Unassigned)
Unconfirmed
Minecraft 1.9.2, Minecraft 1.9.3 Pre-Release 3, Minecraft 1.9.3, Minecraft 1.9.4, Minecraft 16w20a
Retrieved
/summon-ed dragons no longer move.