Barney = Satan

The truth is finally known!

Barney seems innocent and sweet but in fact
he is Satan.

It's all very simple:
1) Start with the given: CUTE PURPLE DINOSAUR
2) Change all U's to V's (which is proper Latin anyway):
CVTE PVRPLE DINOSAVR
3) Extract all Roman Numerals: C V V L D I V
4) Convert into Arabic values: 100 5 5 50 500 1 5
5) Add all the numbers: 666

Thus, Barney is Satan.