Once combat is joined, a person being attacked without warning with a reflexive wits + awareness to get their DV, else it is 0 (pg 155, core)
An attack needs at least 1 threshold success to hit, a skill check doesn't. Bleh
Parry DV can be applied to range attacks unless otherwise specified
1st and 2nd excellencies must be invoked before attack dice are rolled (pg 145, core)
All charms/motes, excepting rerolls, must be declared before any dice are rolled (pg 145, core)
Surprised characters have DVs of 0 against the ambusher(s).