Some creatures are significantly tougher than other creatures, are harder to find and provide a greater reward when defeated. These are known as Boss Monsters.
“The mother of all Spidrox and Spidren. Feared by many. Found in the deepest, darkest places.Queen Spidrox
“A ruler of demons. Bloodthirsty, vicious, and longs for death to come to all that oppose it.Demon Overlord