Mr. Vile

Mr. Vile is a character found inside the giant crocodile shaped hut in Bubblegloop Swamp. Fitting his name, he claims he is the meanest and greediest crocodile of them all. He challenges Banjo's crocodile transformation to try and eat more Yumblies and/or Grumblies than him. The prize after 3 rounds is a Jiggy, but all three rounds are slightly different.
 * In the first round, you must eat more Yumblies than Mr. Vile.
 * In the second round, you must eat more Yumblies while avoiding eating yellow Grumblies that will poison you.
 * In the third round, you must eat both the Yumblies or the Grumblies as indicated by whichever is at the top of the screen.

However, losing a round will cause Mr. Vile to try and chomp Banjo for 2 damage. For an easy, or less difficult, victory, use the Turbo Trainers. Once the Jiggy is earned, Mr. Vile offers a second challenge of playing three rounds for 3 Extra Lives at the cost of 1 life for a loss.

Trivia

 * Mr. Vile looks similar to a Klaptrap from Donkey Kong Country, which is possible due to the fact that the Donkey Kong series and Banjo-Kazooie series were made by the same company, Rareware.