OK so im hosting a Thermos-1.7.10-1558-58 Forge/Bukkit Server w/ the Essentials Plugin & a few other Forge mods... i was wondering why i can't spawn in Mobzilla using a Spawn egg. Every time i try he disappears instantly.. My server difficulty is set to Hard and still.

This is my Server.Properties:

#Minecraft server properties
#Mon Jan 23 23:12:31 EST 2017
generator-settings=
op-permission-level=4
allow-nether=true
level-name=world
enable-query=false
allow-flight=true
announce-player-achievements=true
server-port=25565
level-type=DEFAULT
enable-rcon=false
force-gamemode=false
level-seed=
server-ip=
max-build-height=256
spawn-npcs=true
white-list=true
spawn-animals=true
snooper-enabled=true
hardcore=false
online-mode=false
resource-pack=
pvp=true
difficulty=2
enable-command-block=false
player-idle-timeout=0
gamemode=0
max-players=5
spawn-monsters=true
view-distance=10
generate-structures=true
spawn-protection=0
motd=Minecraft Server

i just don't know whats preventing this...