Bliss might actually be interesting,if so here's my idea of a backstory
The Professor created Bliss before the main ppg we know today as the original idea for the perfect little girl.She was created successfully, but had some emotional problems.She one day got so upset she decided to run away from the Professor leading to Blossom,Bubbles,and Buttercup.She eventually returned as a teenager,but still has emotional problems.I believe that due to seeing images from the episode such as the examples below.
