This page offers a guide on how to get 100 coins in Pianta Village. It is advised that you go into the Episode 5: Secret of the Village Underside as this is best episode for obtaining coins the easiest.
Collecting 100 Coins
Firstly, you’ll want to hatch the Yoshi by grabbing the right fruit from the fruit tree. Then, use the Yoshi to hit down the beehive to the left of the bridge and then attack the bees on the ground, which will earn you a fair few coins (19). Make sure to hop straight back onto your Yoshi when the Beehive drops so you can then use Yoshi to attack the bees. Next, head to the right and shoot the two Pokeys in the ground for two extra coin (21). Near the fruit tree building and the swing, you can also find three more Pokeys, each yielding an extra coin (24). Sometimes Pokeys yield three coins at once, but this is rare and shouldn’t necessarily be relied upon.
Make sure you still have Yoshi as you head over to the palm tree to the left of the bath. Here, you’ll find another beehive that you can knock down using Yoshi’s juice to yield a lot of coins (48). Near the bath, you should be able to spot a large stone Pianta statue. Groundpound on the nose to grab nine extra coins (57).
Now, you will want to head down the hole to the underside of the village that can be found to the right of the bath area. From here, head along the mesh path until you reach the sliding panel. As you slide along the pole using the panel, you’ll pick up an extra 10 coins (67). Continue along the mesh platforms until you reach the mushrooms. On these mushrooms are several circles of 6 coins to pick up. There is a total of 40 coins to be collected on the mushrooms (107). The Shine Sprite will spawn when you’ve gotten exactly 100 and it will spawn near the Pianta statue and the bath.