The launcher opened as normal but when I launched the game itself, it became unresponsive (with the typical message that I think is roughly "Minecraft 1.12.2 is not responding" at the top) for a few seconds, until the Minecraft credits started playing instead of allowing the game's main menu to open. They were not the ones that play after the Ender Dragon fight with the story, but instead contained nothing but full credits to all the creators/developers/everyone else involved in making both the main game and Realms as well as various other jobs like business/advertisement/social media along with a single quote from an unknown author at the end. The quote itself was, "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover." - Unknown. After the credits and quote were finished playing, the window turned black and the game went to the normal starting menu as if nothing had happened. When I asked people on 2 different servers if this same thing had happened to them, they all said no and asked if I played with mods. I do not, and have never downloaded either mods or texture packs so they are not present/involved in my copy of the game. I did not check to see if the credits were skippable, nor did any of this happen again when I quit the game and relaunched it a few minutes later. This has never happened before.