[%c_effect h1;square;h1;type;Interesting;persistent;true] Not a very popular move, but it was played in two important games in 2022 by Ukrainian GM Kirill Shevchenko. GMs Viswanathan Anand and Fabiano Caruana, among others, have also tried this move in older games. The main idea of the mystery king move is to prepare the f-pawn advance and also vacate the g1-square for the white knight, which can maneuver via g1-e2-g3, as will happen in the game. Of course, it's hard to believe that this plan gives White an objective advantage, but what is sought in this line is a middlegame position that allows for the creation of imbalance.
1. e2e4  1... e7e5  2. g1f3  2... b8c6  3. f1b5  3... g8f6  4. d2d3  4... f8c5  5. b5c6  5... d7c6  6. b1d2  6... f6d7  7. e1g1  7... e8g8  8. d2c4  8... f8e8 