Alternative Bosses

Alternative Bosses are anomalous bosses that can be found in seemingly any level in Super Mario 64. They will usually replace the bosses in their course unless there is no boss in the course to replace, though regular bosses not being replaced is not uncommon. It is believed that Alternative Bosses are created in order to change the difficulty according to the player's playstyle.

Examples of Alternative Bosses
Below is a list of Alternative Bosses. Note that these are the most common examples, and are not the only possible examples.

Chain Chomp
Bob-Omb Battlefield's alternative boss is the Chain Chomp, being one of the few examples of Alternative Bosses that are already enemies in the game. The Chain Chomp can appear on top of the mountain, replacing Big Bob-omb, instead of their regular spot. They otherwise function as normal, and will break the gate when the post is ground pounded 3 times.

Queen Thwomp
Whomp's Fortress' alternative boss is Queen Thwomp. It can replace King Whomp, but can appear in separate missions, replacing the tower at the top of the course. It is a pink Thwomp that is twice as large as the regular Thwomp. It attacks by moving above Mario and attempting to crush him. Queen Thwomp can be defeated by punching it when it falls to the ground 3 times. When defeated, it will drop a star.

Unagi
Jolly Roger Bay's alternative boss is the Unagi. The Unagi will function as normal, except that it can swim to the top of the water. To defeat it, the player has to run into it with the Metal Cap 3 times.

Yeti
Cool, Cool Mountain's alternative boss is the Yeti. It can appear seemingly anywhere in the main course. It is a Bowser reskin with white fur covering most of it's body, with it's face being a pale skin color. It attacks by attempting to run into the player, and must be defeated by making it fall off the course 3 times (It jumps up after each fall, similar to Bowser). When defeated, a star will appear from where it fell off.

Mad Piano
Big Boo's Haunt's alternative boss is the Mad Piano. It functions as the brown Mad Piano enemy discoloration, taking 3 ground pounds instead of 1, and is also the same color as the regular Mad Piano. It will explode into a star.

Ghastly Snufit
Hazy Maze Cave's alternative boss is the Ghastly Snufit. It is a large version of a Snufit, but with a purple body instead of a regular Snufit's red. It can appear in the Hazy Maze in place of a regular Snufit. It attacks the same as a regular Snufit, but Mario can punch the bullets to send it back at the Ghastly Snufit, which will damage it. This must be done 3 times to defeat the Ghastly Snufit and make it drop a star.

Flaming Face
Lethal Lava Land's alternative boss is the Flaming Face. It takes the appearance of the flame with a face on the painting, and can appear instead of either Big Bully. It attacks by shooting fireballs. Whenever it shoots a fireball, it gets slightly smaller. It is defeated when it shoots too many fireballs and becomes so small it is barely visible. When defeated, a star will spawn.

Power Pokey
Shifting Sand Land's alternative boss is the Power Pokey. It is a regular Pokey with 10 body segments, and is defeated like a regular Pokey. It can appear in place of a regular Pokey. When destroyed, a star will appear.

Sushi
Dire, Dire Docks' alternative boss is Sushi. It will function the same as the regular Sushi, though it will target the player. To defeat Sushi, the player has to trick it into swimming into the whirlpool in the middle of the area. Upon Sushi being sucked down the hole, a star will appear.

Big Shocker
Wet-Dry World's alternative boss is the Big Shocker. It is a large Amp that can appear in the village section of Wet-Dry World. It doesn't attack, simply doing damage upon contact. Notably, when the Big Shocker appears, the village is not completely flooded upon entry. To defeat the Big Shocker, the village must be flooded entirely, which will make the Big Shocker shrink and then turn into a star.

Rocky Wrench
Tall, Tall Mountain's alternative boss is the Rocky Wrench. It will appear at the top of the mountain and take the appearance of a Monty Mole with a small platform on it's head, and can pop up from several holes. It will otherwise function the same as a regular Monty Mole, throwing rocks at the player, though it will need to be jumped on 3 times to defeat it. However, before being able to jump on the Rocky Wrench, the player will have to take the platform off of the Rocky Wrench's head. When the Rocky Wrench is defeated, a star will pop out from one of the holes the boss can appear in.

Snowy Spindrift
Snowman's Land's alternative boss is the Snowy Spindrift. It is a regular Spindrift with blue petals instead of pink. It attacks by running at Mario, doing damage upon contact. It has to be jumped on 3 times to be defeated, though the player does the spin-jump each time they jump on the Snowy Spindrift. Upon defeat, a star will spawn.

Petey Piranha
Tiny-Huge Island's alternative boss is Petey Piranha. It will appear as a large Piranha Plant at the top of the huge part of the level, not to be confused with a large variant otherwise regularly found on the huge part. When the player reaches Petey Piranha, they simply need to punch it while it is sleeping, making it disappear and turn into a star.

Clockwork Guardian
Tick Tock Clock's alternative boss is the Clockwork Guardian. It's design varies, but usually takes the appearance of a Metal Mario. It functions exactly like Mario, and has to be punched 3 times to defeat it. When defeated, it will explode into a star.

Sky-High Guy
Rainbow Ride's alternative boss is the Sky-High Guy. It is a large Fly Guy with a blue body instead of red. It usually appears at the edge of the course. It will split large fireballs at the player, similarly to a regular Fly Guy. It cannot be defeated, though some have reported it will disappear upon walking past it.

Reportings
''Everything in this section should be taken with a grain of salt. These are all unverified claims.''

Report 1
"I was playing Mario 64 on an old N64 I found in my attic, for nostalgia. Everything was normal until Jolly Roger Bay. I finished all 6 missions but then when I went to get the 100 coins star I saw a 7th mission, "Unagi's Hunt". I selected it and there was this cutscene of the Unagi exiting it's tunnel and clacking it's jaws. I grabbed the Metal Cap and ran down towards it. It started swimming straight towards me, so I ran around it and jumped into it. It recoiled backwards, indicating I did damage, and the Metal Cap wasn't disappearing. I hit the Unagi 2 more times, and it recoiled into a wall, falling to the ground, then coughed up a star. I moved on, thinking it was a special mission I somehow unlocked. When I went into Dire, Dire Docks, I did all the missions again, went to get the 100 coin star, and "Unagi's Return". It was the same as before, except the Unagi had a bandage on it's head. I grabbed a Metal Cap nearby I didn't remember was there and fought it. I defeated it, and the same defeat animation played. Nothing else out of the ordinary happened, and I only recently learned this wasn't a normal occurrence. I don't know why I found the Unagi boss fights, but they were honestly pretty fun."