Horror Head

The second Assassin-type enemy, although despite being encountered much later than the Skull, this monster is pretty much identical to it. The only differences are on its slightly higher HP and different values for some elemental resistances, but still, it shouldn't be much problem to defeat despite its high physical resistance. After all, statistically it's pretty much a Phase 2 monster appearing during Phase 4, where you have access to much more powerful equipments and Hyumas.