One of my favorite monsters to use in Pnp was the Spell Weaver. I good Google search should help you out. My quickie search got me a lot of not what I was looking for results…..
In a nut shell the Spell Weaver is a lot like a the best caster mob ever. It can cast upto 12 levels of spells at the same time. IE 12x 1lvl spells or 2x 6lvl spells or any combination of spells a round to get to up to 12. Often I would have one jump out from around a corner slam someone with 6 different magic missile spells hurl a fireball and then blink away, all in one surprise round.
Do you know what 304d+30 does to a PC with out (night) shield or some other way to prevent magic missile damage? Normally kills them, but might just hurt them real bad. But add in a fireball… Good times for the DM… 🙂
One of the tricks I would have my spell weaver’s do was cast an programed illusion of itself as if it was invisible. Then make it invisible. At the time my players were more or less running See invisibility all the time. And they would burn a few resources fighting a illusion. Well as long as I didn’t over use the trick and until true seeing became a possibility….