So, I really know nothing of TTYD:
This is after a shell toss, NOT A POWER SHELL!
How to do:
Do the action command normally.
Upon hitting the enemy, DO NOT PRESS, BUT HOLD A, keep holding for a while until he starts to slow the spin down.
Release and press A immediately to have him do the finger.
How I found it?
The Japanese version has the Stylish work differently. In the English version, getting the spin of the power shell is one stylish as well as the finger, but this is not the case in the JP version where the only stylish is after the finger so, you do both for a single stylish.
But on the English version, the spin of the of shell toss is one stylish, nothing tells you you can do another one.
I was playing the JP version and the spin of the shell toss didn't gave a stylish, this points out that another stylish existed.
After messing with it, i found that you simply have to hold A instead of pressing it.
Seriously, guys, how well hidden that one was, I doubt a lot knew it.....