The "Dolphin Dancer" achievement requires that I get three dolphins to appear on screen. It seems that the longer I run, the more likely I am to get more dolphins, but I'm curious what actually causes this number to increase. Is it distance, number of fairies collected, number of stars destroyed by rainbow power, or perhaps some combination thereof?
Based from my experiences playing the game:
By this formula it would take 15000 score to get 3 dolphins. Hope this helps