DerSpawns

Really easy to setup, do you need MythicMobs to spawn within a random area? Send a message saying a boss has spawned?
With this plugin you can control how long it takes to spawn it, with a random chance. You can choose the area and even create a WorldGuard blacklist area.

Config.yml

Spawns:
  Dragon_1:
    Name: '&4Reaper''s Pet'
    Region_Blacklist: #worldguard region name
       - "spawn_region" 
       - "pvp_arena" 
    Mob: Dragon_Boss #MythicMobs name for the Mob you want to spawn
    Broadcast:
       - '&4A dragon has ben spotted'
       - '%name_placeholder%: %coordinates_placeholder%'
    Location: #coordinates should make a square, like pos1 and pos2 in world edit
      Min:
        X: 1300
        Z: -2500
      Max:
        X: 2500
        Z: -1500
      World: world
    Timer: #how long in seconds to summon the mob
      Min: 28800 # Seconds
      Max: 28800 # Seconds

Config.yml

Spawns:
  Dragon_1:
    Name: '&4Reaper''s Pet'
    Region_Blacklist: #worldguard region name
       - "spawn_region" 
       - "pvp_arena" 
    Mob: Dragon_Boss #MythicMobs name for the Mob you want to spawn
    Broadcast:
       - '&4A dragon has ben spotted'
       - '%name_placeholder%: %coordinates_placeholder%'
    Location: #coordinates should make a square, like pos1 and pos2 in world edit
      Min:
        X: 1300
        Z: -2500
      Max:
        X: 2500
        Z: -1500
      World: world
    Timer: #how long in seconds to summon the mob
      Min: 28800 # Seconds
      Max: 28800 # Seconds