I would't look to /Mental for a single target monster, it has a strong AoE focus. /Mental does go very well with Ice, but it's because it adds AoE capability and rounds the set out nicely. For a true single target specialist, go Ice/Electric or Ice/Energy and use the melee attacks.
As for soloing AVs, I suspect Mental would be a decent choice. It gives you a regen/recovery boost (though it is of limited use against a single target) which should help keep you healed up provided you have softcapped ranged defense. I'd actually consider /Electric even for AVs though... it has a very high DPA immobilize (which is good because keeping AVs immobilized is important, especially for non-fliers), a damage aura to speed up the fight, and an endurance recovery power (though also limited in effectiveness vs one target). You also get extremely strong melee attacks if you want to risk going the Smashing / Lethal softcap + melee route.
Ice/Mental should be a fun, well balanced set, I'm just not sure how much /Mental adds specifically to AV soloing.
Cascade, level 50 Blaster (NRG/NRG since before it was cool)
Mechmeister, level 50 Bots / Traps MM
FAR too many non-50 alts to name
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Just tpying with a concept and was wondering if anyone had any experience with an Ice/Ment blaster. Seams like the -recharge would be significant and the two cone attacks would compliment nicely. Think it could take an AV?