Bring back the mystery: A rare, elusive stalker mob for end-game survival

Description: Minecraft is an amazing game, but for long-time players, survival has become too predictable and safe. We need something to bring back the original feeling of mystery and excitement. I propose adding a super-rare, mythical stalker mob (inspired by the game's oldest legends). It shouldn't just run and attack the player. Instead, it should have a unique AI: It only appears in single-player worlds, very rarely, at maximum render distance during thunderstorms or deep underground. It watches the player from afar and vanishes into thin air or behind a wall the moment the player looks directly at it. It leaves subtle signs of its presence, like random 2\times2 tunnels, unlit redstone torches, or missing leaves on trees. This would not ruin the game for casual builders, but it would bring a massive spike in popularity, excitement, and nostalgia for millions of veteran players who miss the eerie atmosphere of old Minecraft.