Disenchanter

This blue-furred creature sports an elephantine trunk and a camel-like body. The air around it seems to shimmer with magical potential, and it gazes around with doe-like, intelligent eyes.

Source: Tome of Horror Complete (Sword & Wizardry)
Originally from Fiend Folio 1e. Has appeared in 2e, 3e, & PF.

Cool Factor: Well it's a blue skinned camel with an elephant truck? I guess that is cool. It does drain all your magic items. Now that is cool. That great big trunk is great for sniffing out that magic stuff. Here is a few encounter ideas
-A dwarf comes to town seeking a treasure horde. Only problem is he doesn't exactly know its location. He suggest the group find and tame a Disenchanter. With the help of the beast he can pinpoint what he seeks.
-A town has a herd of Disenchanters. They feed them magic items. They have a great distrust of the arcane and have used this herd to keep adventurers at bay.

Combat: The main offensive ability of the Disenchanter is to drain away magic from items. It tends to target the most powerful one. Although if it is concealed it will randomly target items on the individual. If a magic item is hit by the Disenchanter you get a saving throw. If failed the magic is drained from the item and it become normal.
     On the positive side if all your magic items are concealed or if it targets a specific item it get -6 to attack. The Disenchanter also requires a +1 weapon to be harmed.

Verdict: There is quite a bit you can do with a Disenchanter. They have a nice unique ability that can add some flavor to an encounter or a session. Also if you have given your group too much treasure and need to scale back a bit an encounter with Disenchanter might just do the trick.

Note: There is an ecology article on the Disenchanter in Paizo's Misfit Monsters Redeemed. It is a Pathfinder product but 95% of the material is fluff.

Ioun Beholder

An Ioun Behelder appears as a floating crystalline orb circled by multi-hued ioun stones that trace orbit around the central sphere.

Source: Creature Collection II: Dark Menagerie 3.0

Cool Factor: The iconic ioun stone meets the Beholder. A pretty interesting combination. The Ioun Beholder is essentially a crystal ball with eight ioun stones floating around it. If the Ioun Beholder is encountered without eight ioun stones it remains dormant and acts like a crystal hypnosis ball with the ability to make a suggestion. This mental suggestion forces the players characters on a quest. A quest to find more ioun stones and to activate the beholder.

Imagine delving into a dungeon to find a crystal ball on an altar. It is dormant. Then it invades your mind and makes a suggestion. Find me ioun Stones. I need eight of them to be activated. Right there is an campaign. You have your players character searching the world for ioun stones to activate the Beholder while enchanted.

Combat: In the 3.X system the Ioun Beholder is an intelligent construct. Once it has acquire all eight Ioun Stone it is a fully active creature. It uses the ioun stones as secondary eyes similar to a typical Beholder eyestalk.

-Its a CR7 creature in D&D 3.0 with relatively low Hit Points but a very high AC.

-The floating stones create an rainbow pattern. It mimics the arcane spell. Able to fascinate creatures who view it.

-Eye Rays: Similar to the Beholder Eyestalks. Each of the eight ioun stones can create a ray. The ray has up to 16 different variations. It can do ability damage, blindness, fast heal, absorb spells, etc. A very versatile ability.

Verdict: I have never used the Ioun Beholder. I love the concept behind it. It tends to dwell inside ancient ruins of civilization that have long vanished. An intelligent crystal ball pulling the strings. Maybe sending out minions to search the world for ioun stones. You can have the group encounter goblins raiding a wizard academy. Once questioned they reveal that some being of crystal has clouded their minds with dreams of floating stones.

The whole mastermind angle works well for the Ioun Beholder. It can be a background threat for a few levels while the group tries to piece together clues. Once all the clues are assembled it leads to buried vault in the dark corner of the world. A very cool creature indeed.