It's calculated every to-hit check, as if you had activated an attack against that enemy. So, per mob, per pulse.
50s:
Grimmloch, Tactically Delicious, Ugly Frankie, Operative Tracker, CryoFurnace, Professional Help, Silver Sphinx, Aries Knight, Tachyon Aegis, Jade Sphinx
Currently building:
Any one of half a dozen alts!
I understand Quills has critical hit rolls. Do these happen like damage procs (i.e., every 10 seconds) or is it per mob, per pulse?
Current Triumph Server Fifties:
Jim Pinrail (energy/kin defender), James van der Helm (ill/ff controller), Jim Jab (db/sr scrapper), Golden Chalice (emp/rad defender), Exclamation (dm/sd scrapper), Jim-El (elm/sd scrapper), Riparian (spines/wp scrapper), Psychiatric Solution (mind/psi dominator), Tricky Pick (night widow), Hypohipster (km/wp scrapper)