Yellow Toad is a variant of the Toad species in the Mario series. He has served an important role in the New Super Mario Bros. series, where he was introduced as a playable character to assist Mario and Luigi on their adventures. He has additionally made appearances on more minor scales in sports-based spin-offs, too.
Yellow Toad is practically a palette swap of the original Toad and shares the same physical characteristics as him. The only difference is the obvious inclusion of the color yellow, featuring on the vest and the spots of the mushroom cap.
New Super Mario Bros. Wii
Yellow Toad was first debuted in New Super Mario Bros. Wii along with his blue partner. Both Toads were celebrating Princess Peach's birthday party, only to be ambushed by Bowser Jr. and the Koopalings when they pull out a trick to kidnap Peach. This has prompted Yellow Toad and his partner to accompany Mario and Luigi on their usual adventures of rescuing the damsel-in-distress.
The game has a built-in multiplayer function in which four players can simultaneously play the levels together, with each player controlling one character. In this case, Yellow Toad is controlled by the fourth player.
Towards the ending of the game when the princess has been rescued after Bowser's defeat, Mario and Peach mistakenly leave Luigi behind when they fly back home on their hot air balloon. The Yellow and Blue Toads, however, step in to rescue Luigi from his troubles by offering him a flight back on their balloon, which they've brought along as well.
New Super Mario Bros. U Deluxe