Stalker

The third enemy in the Assassin-type category, and in comparison to all its predecessors, this monster is quite an step up, as its Attack and Defense are the triple of the Skull and Horror Head, and its HP around eight times of them. This, coupled with its nigh immunity to physical attacks, makes it quite a problematic enemy to kill, so the best you can do it's to bid time for your Reyvateil to Purge and reach an ideal Burst value to take them out. However, be careful of their Stored Attack, as the Energy Reduction they can use decreases the speed at which the Burst Gauge increases, increasing the time it'll take you to dispose of these monsters.