Psys and Mentalista are inseparable I guess xD
Anyhow, to be on topic, psys camp white to tank a lot of damage and then put up black to deal high damages. As Cynix puts it, they are "glass cannons". I don't know about mass pk but I've seen psys in 1v1, if you know your skills, you can do a lot of stuff.Same goes for all classes. You gotta know your skills and the perfect combo to use them.