Most important question:

[guineapig]

majin / Mario: The balanced character, Imajin was the perfect fit for a player just starting out. While Mario replaced him, Imajin's balance in all areas has since become a staple of Mario's in the sports games and the Super Smash Bros. Series.

Mama / Luigi: With the ability to jump higher and lightly hover at the top of her jumps, Mama was a good choice for areas with long gaps. Luigi took her place, and in later games he kept his special jumps.

Lina / Princess Toadstool: The perfect character for a player with trouble timing jumps, Lina could hover, although she has low speed and strength. Princess Toadstool replaced her. Lina's moves inspired two of Peach's moves in Super Smash Bros. Melee and Super Smash Bros. Brawl.

Papa / Toad: The most powerful character in the game, Papa could throw enemies and items very far, but he was not very good at jumping. Toad takes his place. This also started idea that Toad may have superhuman strength.