petercordia wrote: If you berserk him 1:1 he should go down
I personally find that using berserk on mennas particularly is slightly higher risk than I'm comfortable with. He will go down a very high percentage of the time, but his shield can occasionally randomly roll well enough to keep him alive through the length of a berserk, and being slowed (or passed out) and silenced and injured in front of mennas is a tight spot to be in.
Usually I forego berserk in favor of other (consumable) buffs for Mennas particularly (because he can both infrequently negate (a portion of) berserk and because he can cut off some of the better escapes if you should fail to kill him) Other things of comparable difficulty either don't have a shield (and so can't randomly negate as much damage) and/or don't prevent you from escaping on the occasions when things go pear shaped.
Naturally if you don't have another way to handle him, then by all means go for it, but there's usually some other method available for dealing with him, even for berserkers.