Shade Crits and Link Skill?

Link skills stack regardless. The Phantom LS will give you an extra % on your base crit rate. The Shade skill tacks on an extra 90% when the monster is below 50% HP. The only thing that stacks oddly, iirc, is the DA and Kanna link skills, as they are multiplicative (someone correct me if I'm way off base).

They used to be weird. Not anymore. They are all considered as Total Damage %(additive to each other) and show onto your range as Range_formula*(1+TD%).