The most important part of this game is the player character. This is the direct representation of the player in the game. The player can control the character and move it around. The player has to protect the character from harm to win the game.
We will look for an interesting sprite in the Scratch library to use as the player character. The diver looks like an interesting choice since he is lying horizontally and facing right.
A perfect start for a side-scrolling game! The diver can be found in the People or Underwater category. There are two diver sprites. I choose the orange one, because it stands out better against a blue, watery background.