I have found out that frog's tongue may have a use. When you stand beside a wall, it will go through it! You shouldn't make more than 1 tile widht of that wall (in simple tileset like Castle or Carrotus, tilesets like Medivo need to check out yourself), so it will work. With that tongue you can pick up goodies and react with Trigger Zones or Rock Triggers, so that to continue on or gain stuff you have/want to become a frog!