Whenever Pepe tells you that you've opened a new level or boss.
The chime that plays when you collect a Muppet Token.
Scrappy Mechanic: The health pickups are cute little Muppet hearts with wings... that actively avoid being picked up, and are often placed in areas where you could get hurt trying to catch one.
That One Achievement: Racing Willie in Escape Claws. He's wicked fast and it doesn't help that the level has a lot of bottomless pits, leaving you little room for error.
That One Boss: The Goulfriend's boss fight where you slide down a hill three times and try to avoid the holes she punches in the earth. Not surprisingly, each part is more difficult with the third involving penguins pushing a block of ice your way.