Blargg's Boiler

Blargg's Boiler is a subterranean cavern found somewhere between the Bone Dragon Pit and the pipelines in Yoshi's Story. It is completely flooded with lava, and so the only way to cross is by traveling atop the bridges of giant bones.

The cavern is the native home of the Blarggs, which make their only appearance in this level. It is also the home of Spark Spooks, Lava Ghosts, and Puffers.

The hidden Heart Coin letter for this stage is E.

Layout
The level is entirely horizontal, with no vertical platforms to climb upon; instead, the player must balance across Bocci Balls and walk across bridges made of bones, which bend when stepped upon. Spark Spooks and Lava Ghosts pop out of the lava frequently, making it difficult to know when to walk. Additionally, the level is relatively dark with the only source of light coming from the lava. As the lava oscilates, the brightness of the level goes up and down. Almost all the Melons of this stage can either be found in ? Bubbles or by sniffing the ground; for this reason, the official Nintendo Power Player's Guide describes it as the easiest level to collect Melons from.

At the start, there is an Egg Block over two consecutive bone bridges, alongside 2 coins and 3 fruits. The player can use the eggs from the egg block to defeat the first Blargg, who pops out at the end of the second bridge. Once defeated, the player can move on to the next few bridges. A gap with 8 coins above it appears after the third bridge, with the first Miss Warp located right next to it. On the fourth and fifth bridges, Fly Guys first appear, and carry melons for the player to try and take. A Message Block also appears between the fourth and fifth bridges. After this, a gap with a Melon above it appears, with the second Blargg popping out of the lava. If the player ground pounds on the edge of the gap located to the right of the Blargg, a line of coins will appear above the next bridge. A Puffer also appears on the sixth bridge, initially invisible until the player walks next to it. The seventh bridge has 5 fruits on it, while the eigth bridge has a single Melon trapped in a Bubble; the third Blargg emerges when the player eats this Melon. The ninth bridge has 3 fruits, with 2 Lava Ghosts emerging to try and attack the player. At the end of this bridge is the first Vase of the level, located next to the second Miss Warp.

The second part of the stage contains no bridges. Instead, the player must traverse through individual bones at the beginning. Spark Spooks jump out of the lava at certain intervals. On the first pair of bones is a ? Bubble, which contains 5 jumping Coins when popped. The first bocci ball can be found after the first set of bones, with three fruits (one of them being a melon) overhead. After this, another pair of bones with an Egg Block above them can be found, with a Melon hidden nearby; the third Miss Warp can be found after the small gap to the right of this. The next melon is also found next to the third Miss Warp, located inside a bubble. Following this is another set of bones, alongside the fourth Blargg, a ? Bubble, and an Egg Block. After the Egg Block is the second bocci ball, with three Fly Guys flying over it. Each of the three Fly Guys carry a Melon with them.

At the end of this segment is a bone with a blue Warp Pipe above it, which takes the player to the Special Delivery minigame. Here, the player must carry 7 Melon Boxes to the end of the level, while walking up & down a hill with two Shy Guys. A White Shy Guy appears in a ? Bubble here, near the top of the smaller peak. Going into the vase at the end of the level takes the player back to the second part, after the platform section to the right of the original blue Warp Pipe. Along the platform section, the first five Flatbed Ferries move horizontally, with the last two moving vertically. The fifth and final Blargg appears here, but this time, it moves toward the player instead of staying in one place. After the last Blargg, the level finishes up with some more bones and the final platform. The platform contains a Vase and the fourth Miss Warp; going into the vase takes the player back to the start of the first part of the level.

Special Heart locations

 * The first Special Heart is located after the third bone bridge in the level, right under one of the bones making up the gap. A single Spark Spook appears right next to it. The player can either eat it with their tongue, throw an Egg at it, or stand on the bone above it to collect it.
 * The second special heart is found on the second part of the level, blocked by the fourth Blargg. The player must shoot an Egg at the Blargg, and then at the Special Heart, in order to obtain it.
 * The third Special Heart is located near the end of the level, underneath the last movable bone. To obtain it, the player must stand on the bone long enough to lower themselves onto the heart, and then touch it.

Storybook segment
''As the page turned, an ocean of boiling hot lava bubbled out. If the Yoshis didn’t cross, they would never find the Super Happy Tree. Blargg and the lava were scary. The Yoshis bravely fought their way through.''