Burt the Bashful is a character making his debut in Super Mario World 2: Yoshi's Island. He is the first boss in the game.
Burt used to be a regular Burt until Kamek made him huge. Burt The Bashful is a big Burt Bro that tries to defeat Yoshi by jumping on him. in Yoshi's Island DS, he is replaced by the Big Burt Bros.. The level Burt The Bashful appears in Burt the Bashful's Fort.
Super Mario World 2: Yoshi's Island
In the battle, Burt bounces by jumping Yoshi. Yoshi has to throw the eggs at Burt until defeated. After being defeated, Burt loses his pants (somehow), turns bright red, and flies about like a balloon (possibly to flee) and disappears.
Yoshi's Woolly World
Burt appears in Yoshi's Woolly World. He retains his attack pattern from before, but this time, Yoshi has to use his tongue to pull on Burt's pants. Just like in his first incarnation, Burt turns bright red and blows air and rockets away in an attempt to flee.
Burt returns in the game as Burt the Ball, having been turned into a literal beach ball.