I REALLY hope beating the minigames isn't required to unlock anything like a "best ending" or something, because I have no idea how to unlock them. I unlocked the night 4 minigame by complete accident, and I can't beat it to save my life (because it's just Undertale and I suck at Undertale)

You don’t have to beat the mini games to get a best ending. You do have to play them to get a star though.