There's a one-time surefire method and two not-so-certain ways to kill your Magikarp.
How to get event 31, "Hop, Skip & Whump!" and feed a hungry Pidgeotto in Magikarp Jump.
Check this guide for all the info on support Pokemon and Friendship items in Magikarp Jump!
How to fish up a Dratini and net event number 32.
This guide has all the info on the different patterns in Magikarp Jump and how you can get them!