Forest Maze
Get the Croaka Cola hidden chest on first screen
In the Wiggler Jump room, grab the quick Mushroom on the left (to be used in a later fight)
Do 4 Wiggler Jumps. This requires you to bounce on a Wiggler 10 times before it goes back underground. Its movement pattern selection is entirely RNG. (If you've missed any Frog Coins before this point, do an extra Wiggler Jump per Frog Coin you missed. You should finish here with 12 frog coins if you chose to grab the Mushroom Kingdom frog coin chest, and 11 frog coins if you chose to wait until after Bundt.)
Get the hidden Frog Coin chest after the exit of the first underground area
Get the Croaka Cola hidden behind the first sleeping wiggler
Get the Red Essence in hidden chest before the save point
(video credit: IamTehShark)
Level up (if you got less than 19 dogs):
Mallow [4] - SP