More NPC Work

If the level is set to -1 (it can also be 0 too), then the spawn service will automatically generate a level between the min level and max level. Otherwise, it will just use the level.

if (level != -1) creature.setLevel
else, it will create a new instance of Random and randomize between the min and max level.

So having the level at 13 will only spawn level 13 desert demons. Min level and max level will not be considered, so you can probably just remove them.