After many attempts to defeat the Level 7 Gauntlet boss Bowser X, I was finally able to defeat him only after leveling up the Mario Bros. to Level 60. He was an annoying boss as he will inhale my Special Attacks after I use them against him, forcing me to use less-powerful attacks and the fact the Mario Bros. will have to pass a fiery obstacle course whenever he becomes giant. Around the time I defeated Bowser X, I learned how to defeat the previous bosses with less turns and using less Special Points. Defeating the Level 1 boss Durmite X was easy and it took me one turn one turn to defeat her.
Even though I finally defeated him, I am somewhat disappointed that I was awarded 25,000 coins instead of a rare item as I no longer have use of coins. Anyway, I am satisfied that I finished one of three Challenge Node games even though they are not necessary to complete the game. I already completed the game days ago without them.
With leveling up the Mario Bros. to Level 60, it made defeating the last boss Dark Bowser easier. I already defeated him the fourth time this morning.