I was asked to help with the porting of Freeblade to tvOS. There were a few things involved with this, the immediate thing was to ensure that the control system functioned using the Apple TV's touch remote.
The larger task was to update the iOS builds of the game to use a different cloud storage solution for use with their savegames, as it was required that a user be able to play on both iOS and tvOS with the same data. This involved creating a detailed plan of a migration for iOS users, as well as proof of concept for the proposed save solution, before attempting the implementation. It was planned to be a phased rollout, with a small cohort going through 4 phases to check compatibility before performing the migration for rest of the users.
Unfortunately a bug which didn't present itself until it was in the wild caused problems and the need to push out a subsequent quick patch for this. While that result isn't my proudest moment, it has re-emphasised the need to do rigorous QA on anything that gets pushed live.