This super compact mod does just as the title describes. It spawns Ender Dragons in the end to an unlimited extent.
A simple config lets you decide how often to spawn dragons in the end, and whether they should generate linearly (a dragon will spawn once every x chunks) or randomly (a dragon has a 1 in x chance to spawn for every chunk that is generated).
Great for server packs that use infinite end generation mods (Endless End, HEE, etc) or don't reset their end as much as they would like to, leaving players out in the dust for months at a time.
