School of Transmutation: Shapechanger, What Do I gain from the Beast besides stats...

[Krotchrot]

As per the Polymorph spell in the book, but I can only turn into a CR 1 or lower Beast. When I do this, I understand that a lot of my things are replaced:

"The target's game statistics, including mental ability scores, are replaced by the statistics of the chosen beast. It retains its alignment and personality."

I'm getting ready to play in an Evil game and I was going to play a Wizard, and my thinking would be to spy on individuals that would go against the party (or my) plans. I was thinking two routes of mischievousness: School of Transmutation or School of Illusion.

My flavor leaning right now is to Transmutation, and I had a cool thought of being able to use the Shapechanger feature to turn into a Cranium Rat. The Cranium Rat has the following which I wanted to clarify if I get these with using said feature:
Senses: Darkvision 30ft., Languages telepathy 30ft., Illumination and Telepathic Shroud. The spell and subsequent errata has no mention of this.

[Whyrocknodie]

Wouldn't you have to polymorph into a normal rat and have a mindflayer bombard you with psionic energy to become a cranium rat?

[MagneticKitty]

Wouldn't you have to polymorph into a normal rat and have a mindflayer bombard you with psionic energy to become a cranium rat?

If cranium rats can breed to make other cranium rats (which I don't know if they can) then I would assume no you don't need that.

[Krotchrot]

It says that mind flayers create cranium rats, but it doesn't implicitly say they aren't found in the wild (breeding) or solely created only by mind flayers.

Besides the obvious of using the feature to turn into a normal rat or bird, I feel the Telepathy could be really handy, combine that with Telepathic Shroud and you are a great spy.