Munster is the easiest boss in Rookgaard. It spawns randomly (tipically only 1 per day)
Treat it like a Diabolic Rat, at lvl 15+ you should be able to kill Munster easily
Munster loot may vary from some platinum coins, gold ingot, etc. It use to drop very rarely Boots of Strong Haste but its unknown if its possible to still drop them.