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.