adds lurker of the night
to make it work as intended:
put a command block where you want it to spawn every night
set it to needs redstone and impulse
connect it with redstone to an inverted daylight sensor
in command block put command "spawnlurker"
when it is night it will spawn
to make it go away in the day:
make command block anywhere
connect command block to normal daylight sensor
in command block put command "kill @e[​type=ln:lurker_of_the_night]
enjoy being massacred if your outside at night!