The Horror check is simply a Will save at DC 10.
While the DC for the Horror check is always the same, the outcome depends on the severity of the fright. This is categorized by the horror levels minor spook, medium shock, great fright, and horrific terror.
The outcome of a failed Horror check is determined by rolling a 1d100 on the Horror Table and checking the results against the column apprpriate to the horror level.
If the player rolls a critical failure (natural 1), roll on the Horror Table at the next higher level (for example, if the character critically misses a roll for a minor spook, roll on the table as though he’d missed a medium shock check).
If the player rolls a critical success (natural 20), the character has become hardened and gains a +2 circumstance bonus on future Horror checks for the remainder of the session. A character may not benefit from more than one hardened effect at a time.