Ok, here I just beat the level. In order to beat Wigglers Red Coins, you must...

1) Go through the painting to th right hallway in that room. It will make you pint-sized.
2)Go through the hole in the rock mountain to come to an ocean/lake thing. Then, defeat Lakitu and Fly Guy (Lakitu because his hovering drone is a PIA, and Fly Guy 'cause he's a PIA.) Then, Go to the cannon on the other side. Don't Get Eaten By Cheep-Cheep!!!
3) Direct the cannon where you see the tip of the mountain on the bottom. ANY WHERE ELSE WILL NOT GET YOU TO THE GATE!!! Launch up there.
4) Walk across the plank to the hole in the mountainside. (NOTE: WALK SLOWLY TO REACH IT!!)

That's only the 1st part. The coins are scattered all over the place, one coin on every landpiece. Take the first coin, next to the Red Bob-omb, and take the coins clockwise around to the entrance. Go to thethird coin's land piece and jump (NOTE: IN ORDER TO GET ALL EIGHT COINS, USE YOSHI WITHOUT FINDING THE RED CAP!) With Yoshi, no one else, jump and hold down B. This is his flight kick, which propels him higher in the air. Get the final coin. Upon getting it, the star will appear. Drop down from there and collect the star.

Hope it helps. It worked for me!