Boss

A Boss is an enemy that Koopa, Goomba or Shy Guy must fight in order to advance. They are in general, stronger than the usual enemies and require a certain strategy to defeat. There are 5 bosses in the first game, and 8 bosses in the second.  

Bosses in A Koopa's Revenge

1. Wario, decked out with a fireball shooting cannon at the exit of Bowser's Castle.
2. Peach, deep within the natural elegance of the lush Mushroom Forest.
3. Waluigi, piloting the Dastardly Doom Drill atop the blanketed snowy peak of Sky Mountains.
4. Luigi, inside one of the many ancient pyramid tombs of the famously arid Dry Desert.
5. Mario, controlling a titanic mech suit on the roof of his long-unoccupied castle.

Bosses in A Koopa's Revenge 2

1. Popmo, at W1-6. (Mario's Villa)
2. Saladro, at W2-5. (Forsaken Pyramid)
3. Umbreltar, at W3-4. (My Name Is Jonah)
4. Burgerstein, at W4-6. (The Jolly Toy Factory)
5. Flying Spaghetti Monster, at W5-2 (Mario's Doomship)
6. Mario, at W5-3. (Mario's Castle)
7. Monstario, the second form of Mario.
8. Final Confrontation Mario, Mario's third and final form only accessible after collecting all the Star Coins and saving the seven Koopalings.
9. Dan Hibiki, at W5-3 without pressing any of the gigantic Switch Palace switches or saving a single Koopaling. Is also seen in boss rush so you don't have to start a new game.
10. King Yoshi, exclusive to Boss Rush.

Trivia

• In v2.9, The boss skins options were removed but to get the option back, Go to the control settings and select "Cancel" or "Apply Changes" to get the option back.
• King Yoshi used to have a door that'll lead you to his boss fight but was later removed