A Challenge

 is a random encounter in Magikarp Jump.

Dialogue
Event Trigger Text: Oh? Hold on. It looks like someone is heading this way.

Mayor Karp: A letter has come for you from your next opponent in the league!

Shall I just open it up for you? Hmm, hmm... Oh! But this is... It's a letter of challenge!

Why, the nerve- Now there's no way you can lose that next battle!

Results
Magikarp seems all fired up now! Its JP went up!
 * Gain Jump Power