Butterfly Winner Achievement in Michael Phelps: Push the Limit
Awarded for winning a Butterfly race in career mode.
How to unlock Butterfly Winner
The first Butterfly race of career mode is available in Season 2. You must win the race (finish in first place) for this achievement. Before the race is a tutorial that you have to do but can skip once you select it. It is advised that you briefly go through it though to learn the techniques that you will need for all of the Butterfly races.
See "Pool Legend" for some tips on how to perform better in career mode.