Passive Ability details for Undead Killer  

As of the december patch, all "killer" and "circle" effects now add an automatic paralyze-like effect to the referred-to mob type. It gives a "[mob] is intimidated by [player]'s presence" message. Note that dragoon-type mobs can use this against dragoons' wyverns also. Killers and Circles and Paralyze can all be stacked. Circles last 1 minute and can be recast every 10 minutes. This information is from Squaresoft's patch notes (except the stacking part, that's from my experimentation).