Blue Yoshis (also called Dark Blue Yoshis) are a color variation of the Yoshi species.
Super Mario series
Super Mario World
If a Yoshi of any color manages to find Yoshi's Wings, it will turn into a Blue Yoshi and fly up to a bonus stage. After Mario and the now-Blue Yoshi complete the bonus stage, the wings will be lost, though the Blue Yoshi will retain its new coloration.
In the Game Boy Advance remake, Super Mario Advance 2: Super Mario World, a Yoshi will not change its color upon finding Yoshi's Wings. Also, once the Baby Blue Yoshi from Star World is found, Blue Yoshis can be found in lieu of where Green Yoshis normally are if Cape Mario hits a ? Block containing a Yoshi Egg.
Super Mario 64 DS
In Super Mario 64 DS, the third player in VS. Mode controls a Blue Yoshi. Blue Yoshis don't have any unique ability in the game, as all Yoshis have the same abilities.
New Super Mario Bros. Wii
New Super Mario Bros. U
Though general Blue Yoshis don't appear in New Super Mario Bros. U, blue-colored Baby Yoshis known as Bubble Baby Yoshis do. They have the ability to spit Bubbles at enemies, turning them into Coins, a Power-Up or a 1-Up Mushroom.
Super Mario World 2: Yoshi's Island / Yoshi's Island: Super Mario Advance 3
In Super Mario World 2: Yoshi's Island, a Blue Yoshi is playable on the Castle of every world, except for level 6-8, King Bowser's Castle; in which a Green Yoshi takes his place. This makes Blue Yoshis the least-used of the Yoshis.
Yoshi's Woolly World
Blue Yoshi appears in Yoshi's Woolly World as an unlockable Yoshi design. After defeating Mega Baby Bowser in King Bowser's Castle, the player unlocked various colored Yoshi designs, with Blue Yoshi being amongst them.
Super Smash Bros. series
Blue Yoshis also appear in the Super Smash Bros. series. Although not playable in Super Smash Bros., a Blue Yoshi appears with the Yoshi team in 1-Player Mode. In Super Smash Bros. Melee, Super Smash Bros. Brawl and Super Smash Bros. for Nintendo 3DS / Wii U, Blue Yoshis appear as a recolor for the regular Yoshi. A Blue Yoshi also represents the blue team in team battles. A Blue Yoshi also appears as a Sticker in the third installment of the series.
Paper Mario series
In the sequel, one of the Yoshi Kid's colors is blue. The Blue Yoshi Kid will be obtained if the amount of time that passes between the point where its egg joins Mario's party atop the hot dog stand to when Mario eventually meets the newborn dinosaur after running from the Armored Harriers is between nine and eleven minutes.
Mario Power Tennis
In Mario Power Tennis, Yoshi can change colors every time he performs a Rolling Egg Return, provided the player has completed the Flower Cup with any character. One of the colors that Yoshi can turn into is blue.
Mario Super Sluggers
In Mario Super Sluggers, a Blue Yoshi makes its baseball debut as a color variant for Yoshi. In Challenge Mode, a Blue Yoshi can be found in Yoshi Park. It gives the player several questions in order to figure out the combination for the gate. Afterwards correctly answering the questions, it will join Mario on his quest. The Blue Yoshi has the weakest batting abilities among all Yoshis, but that is compensated by its pitching, where it ranks first among the Yoshis (being tied with the team captain Yoshi).
Mario Sports Mix
Mario Tennis Open
Mario Kart 8
In Super Mario World, Blue Yoshis had dark blue skin, orange gloves, brown shoes, and a brown saddle. For the sequel, Blue Yoshis' look remained almost the same, but the shoes were recolored purple while the saddle was recolored red. The shoes' color was changed again for the Game Boy Advance port, this time to pink.
From Yoshi's Story and on, Blue Yoshis have appeared with magenta shoes and a red saddle. In Yoshi's Island's sequel, Yoshi's Island DS, and Yoshi Touch & Go, the skin tone for Blue Yoshis was darkened.
Notable Blue Yoshis
Official profiles and statistics
Super Smash Bros. Brawl Sticker information
Mario Super Sluggers profile
Super Mario Run description
"Yoshi is Mario's loyal adventuring buddy. He can Flutter Jump, and he's got no fear of spikes! Popular with Blue Toads."
List of game appearances
Names in other languages