Skull

The first in the Assassin class of enemies, as its name says, this monster is pretty much an improved version of the Assassin mini boss you encountered near the start of the game, and as such, it has its same properties: it's almost immune to physical attacks, and although the elements added to the attacks by Purging can cause it a decent additional damage, it would take a long time to kill it due to its high HP amount, so the best way to get rid of it would be using Song Magic: you can go out of your way using a Lv. 3 Purge or Flipsphere, but normally, just using a Lv. 1 Purge should suffice to kill them. However, be careful to not let them use their Stored Attack Beat Down, as that would make you take longer to kill them due to requiring a longer time for the Purge Ready status to be reached.