Bouncing on one wiggler up 10 times before it despawns will grant you a Frog Coin.
This tutorial video by Sean provides a good overview.
Align Mario by running right towards the nook in the bushes.
Slightly after the Wiggler turns his head (going either up or down), jump on his head. After this initial jump, hit slight left. Ride the Wiggler for about 5 more jumps, then adjust inputs accordingly based on the position of Mario's shadow.
In general, practice the d-pad directions you will use to control where you go when the wiggler turns.
For best results, although you may want to run-jump to land on the wiggler initially, most people recommend not holding Y during the rest of your bouncing.
Here's how it looks in action.
(video credit: Lack)