I'm currently level 17, so I still have plenty of room to shape my skills however I want. Right now I've been focusing on Destruction and Archery, but I've been heavily considering delving into Illusion. I have essentially no experience with Illusion spells, so I had a few questions:

(1) It is my understanding that spells such as Frenzy require both hands to cast. Does the Dual Casting perk have any effect on the power levels of such spells? If, so has anyone found what exactly the effect is?

(2) With the level spells having level caps (i.e. the Master spells like Mayhem work on enemies up to level 25), has anyone encountered enemies that they simply do not work on? This is assuming you have all relevant perks like Kindred Mage and Animage. I'd imagine there are bosses that ignore Illusion spells, but I'm concerned that at high levels there will be groups of enemies that may be too powerful.

(3) Can anyone share the locations of the Master Illusion spells (Mayhem, Harmony, Hysteria)?

bump

I believe duel casting makes the effect last longer.

Dual casting also helps it effect higher levels. The problem with illusion is that before 90 skill, it's not useful in most dungeons. I've encountered undead more than half the time.

Not only that but until you get to your skill to the expert level the spells you have only effect really weak enemies, so it looks like there is a huge viability gap in it. Decent when you start out, svcks for a while and then decent again. I mean calm effects what level 6 guys, even with animage etc you wont be hitting level 20's. So if you are like the OP and leveled with other skills it will do nothing for a long, long time.