Most villans have senshi equals, and ParaPara's no exeption. Here's the list of why Sailor Mercury and ParaPara are equal.
1) They're both BLUE. Blue hair, blue outfit.
2) If you go by colors, all the senshi have a match. (CereCere and Venus aren't as obvious, though)
3) They're both the brains of their group.
4) They attack each other/fight. (Usually the senshi and villan equals will face off)
5) Look at Mercury's equal in the R season and what she has in common with ParaPara: blue hair, cool hair style, blue eyes, blue outfit (with a spce to show off the chest).
6) One of ParaPara's anime attacks is Blue Billard Ball. Blue. Blue's Sailor Mercury's color.
If you aren't convinced, I don't know what will convince you.
1) They're both BLUE. Blue hair, blue outfit.