Make Way for King Bowser!
From the Super Mario Wiki
Make Way for King Bowser! is the final level of World 6 in Yoshi's New Island, and by extension, the game. It can only be accessed after the player has completed all of the main levels without using the Flutter Wings power-up.
Green Yoshi starts the level from a platform on the lava, near Bowser. He frequently summons Metal Guys that Yoshi must swallow and throw at Bowser. Repeating this process three times will defeat Bowser, but suddenly, Kamek appears, growing Bowser to giant size. The player must then combat with Giant Bowser in a battle similar to the one with Giant Baby Bowser from the previous level, but more difficult. Once Yoshi throws Mega Eggdozers to Bowser's mouth three times, he will finally be defeated. Yoshi then can find Baby Luigi by walking to the right, and the ending rolls.