turf
    icon = 'Environment.dmi'

    Entered(atom/O)
        var/area/AREA = src.loc
        if(ismob(O))
            var/mob/Player = O
            if(Player.client)
                var/SpawnChance = rand(0, 100)
                if(SpawnChance < AREA.SpawnPercent)
                    var/Monster/ToSpawn = pick(AREA.MonsterList)

/* Instead of spawning the actual instance (depleting the list), spawn a copy of the monster in the list. */

                    var/Monster/Spawn = new ToSpawn.type
                    var/turf/SpawnLoc = pick(view(O))
                    var/area/SpawnArea = null
                    Spawn.Move(SpawnLoc)

                    if(Spawn.loc == null)
                        del Spawn
                    else
                        SpawnArea = SpawnLoc.loc

                    if(!isnull(SpawnArea) && SpawnArea.Safe) del Spawn //Error line

                for(var/Monster/Sleeping in view(src, 20))
                    if(Sleeping.Idle || get_dist(src, Sleeping) > Sleeping.Attack_Range) continue
                    Sleeping.AI()

            else ..()
        else ..()

mob
  Move()
    src.Moving = 1
    ..()
    src.Moving = 0 // Pretty sure this line isn't reached but whatever.