World 9-4 (Super Mario Bros.: The Lost Levels)
From the Super Mario Wiki, the Mario encyclopedia
This level takes place entirely underwater. The player will encounter a Goomba, Koopa Troopa, Buzzy Beetle, green Koopa Paratroopa, Hammer Bro., and a Blooper before coming to a series of arranged blocks. The blocks read the Japanese characters "アリガトウ!" (Arigatou!), or "thank you", as a message to the players. Between the ガ and the ト is a red Koopa Paratroopa, and between the ト and the ウ is a Lava Bubble. After the exclamation mark is the Goal Pole.
Depending on the version of the Super Mario Bros.: The Lost Levels game the player is playing, the level progression differs after reaching the Goal Pole. In the original and Famicom Mini versions of the game, the player will return to World 9-1 and continue playing World 9 until they run out of lives. In the Super Mario All-Stars version, the player moves on to World A.