JackSparrowYAY
As Walnut said, you need to know how to play a class. I used to enjoy playing a mentalist because of the damage they deal. I found out that I could one shot K.O many forcemasters very easily in duels, before they even had a chance to start casting their ultimate skill Asalraalaikum. So I began to to maximize my mentalist's damage. I found it amazingly fun running around 1-2 shotting those in the arena who hadn't imagine a mentalist being able to kill them (except templars and some STA mentalists), and the best thing in my view is that the harlequin's and forcemaster's aurum give a ICD bonus of 1000% or so, which is pretty good for mentalists. With Blink Pool, I could avoid getting HoP'ed and asaled, and when I blinked around, almost nobody could kill me because they lost me as target. So I once ended up having 3 forcemasters, 1 harlequin and 1 templar chasing me. Though I had to give up and leave the Arena, because it got harder to survive after a while xD
Anyway, I think it might be a good choice going for INT mentalist instead of the STA type. This is because with INT, you can easily kill people when they have to stop in order to hit someone with a deadly skill. This is the moment when your small or big charged magic balls hit your target, and they die. The downside with the INT mentalist is that you have to avoid templars at all cost, or else you'll die by their reflect. In addition, you need to survive before the magic balls hit your target.
The STA type mentalist on the other hand, can survive HoP's, but have a hard time surviving asals, as they can hit more than the max hp of a mentalist. And since there are so many forcemasters jumping around the siege arena, I find it better to go for the INT type. Otherwise, if you have a lot of RPs and/or DPs, try the switch type (macro) mentalist. Use INT when you attack, then switch to STA for survivability. I have no idea if this works, though, because the damage might depend on how much INT and ATK rate you have at the very moment when your magic balls or skills hit your target.
If there are any other mentalists out there wanting to add infos or correct something, that would be great!