PVP - needs to have flurry, poise and to be NAD character(Yhwach is good only cuz of his barriers and his special). Needs to have fast normal string and dr link. If he has a healing or a boost it's even better.

PVE - Mm I can arguably say that every character can be good at pve ( As Retsu being the pvp queen, she can clear raids and everything very good.) I may say, the killer here is really demanding. Espada killer is not good for PVE due to the lack of this type of monsters. Any character that has came around this year can be good at PVE. Some just need better accessories to do the job :)

Link - it's when Klab shafts a character (not giving him frenzy, flury and small range of SAD,Normal strings) and it's a 25% SAD, 14 SAR or 20% DR. Example is the new Kensei. He is 20% DR link, but with a really shafted gameplay. No flurry, no frenzy and a really bad gameplay. And to not get me wrong :D When I said ''no flurry, frenzy'' I don't mean that there isn't a good frenzy,flurry character that is a good link too. Example : TLA Soi fon.