One time I went in a dungeon, with using a specific overhall mod and supreme magicka.. and I ran into a conjurer that summoned 4 mobs.. Mind you I was lvl60 at the time with my own devastating arsenal of magic.
I died so fast =P.
The strangest game experience I ever had also involved magic. I was finding that my current character's conjured creatures were dying within a second of appearing, and couldn't figure out what was going on. I thought at one point that perhaps my saved game had gotten corrupted, so I made a new character, and took them for a walk through the introductory dungeon.
I was surprised to discover a few more summons than I expected along the way, and narrowly survived after dying several times. Then, in the final area, before leaving, I saw *21* demonic princes, just standing around, along with 6 enemy mages. The AI was having trouble managing the numbers, so nobody was attacking anything, but still...
I ultimately traced the problem to a seemingly innocent little mod that added a much greater range of sounds to accompany magic effects. One version of the file was supposedly safe with SM, but it wasn't, and the sounds were not playing with conjuration spells. So these spells were being cast by the AI, but the sound mod assumed they weren't, triggering a recast, which wasn't acknowledged by the sound mod, which triggered another recast, etc.
I substituted a supposedly less SM-specific sound mod, and never had these problems again. But I still have this image in my head of those 21 demonic princes just standing around, as though they were all attending a conference.