Question: In trying to set reasonable limits on a PC's usage of the polymorph chain of spells. Is it plausible to require that the PC have some form of interaction with the target creature? Or can a PC polymorph into a creature that the PC has only heard about? Or read about in a book? Or seen just a painting of? From a solid role-playing standpoint, it seems reasonable to require that a) the creature exists in the multi-verse that the DM is running, and B) the PC has some knowledge of the creature. What is the minimum "knowledge" that the PC must have in order to polymorph into such creature?

Answer: 
Yes, it is plausible to restrict polymorph to creatures that the players have encountered. This is one of the commonly discussed polymorph house-rule.

I think the minimum knowledge would be determined by a [knowledge skill](http://www.dandwiki.com/wiki/SRD%3aKnowledge_Skill) check for that monster. If the monster does not exist in your multi-verse this check would be impossible to complete. Basic knowledge of a monster starts at 10+HD, but I would extend this to be 10+HD+X, where X is creature dependent (maybe based on the number of special abilities the creature has).
Once I used a table based on the teleport tagert table, it was something like it:

```
Familiarity          Fails/Wrong Monster     Weak Version     Exact Monster  

Very familiar                                 1                 2-20       
Studied carefully     1                       2-3               4-20      
Seen casually         1-2                     3-5               6-20
Viewed once           1-4                     5-8               9-20 
Read or saw picture   1-8                     9-15             16-20
Monster doesn't exist 1-19                    20

```

With fails/wrong monster I would jut choose some monster or animal visually resembling the monster but very weak, or totally opposed thing, "So, let me see, you turned into a... Giraffe..."...

A weak version could be the same monster, but without power, or attributes modifies reduced, like instead of +8 in Str, you get +2, etc..

You could fine tune the checks using the CR of the target and the caster level of the character