The anniversary update for Rectangle Guy is here (and maybe a bit late whoopsies). It includes a brand new epilogue to the game's main story called "Warden on the Job".
Warden on the Job includes 5 challenging levels and a new boss, and is meant for players who have already beaten the main story of Rectangle Guy.
If you've already beaten the game, you can jump right into the new update, just check out the "Unlockables" menu. If you haven't beaten the game yet, well, you got some work to do.