Bagpuss
Legend
Here are the Prerequisites...
"Prerequisites: Living creature, level 11, Charisma 13"
Reading it I can see the reason behind the level requirement-
You don't want a heroic monster doing "20 ongoing psychic damage" for example. Because it will finish of the party in short order.
Also the Charisma requirement is because all it's attack powers are calculated on Cha. IE: "2d6 + Charisma modifier" If it had a negative modifier then it wouldn't be a credible threat. I suppose you could put it on any creature as long as you increased it's Cha to a positive modifier.