Unagi, is an eel species found in the Mario series. Unagi is found initially in Jolly Roger Bay, the third level of Super Mario 64. While it is impossible to defeat the Unagi, it is needed to obtain two stars from Jolly Roger Bay.
Touching Unagi will deduct three points of Mario's HP.
In the next mission Unagi is seen residing in a hole on the ocean wall, Mario can lure him out by going near. The Star is on Unagi's tail. Mario can get it my making contact with the Star.
In later missions, Unagi simply circles the drop off.
New Super Mario Bros.
They later appear in New Super Mario Bros. in underwater levels as regular enemies. They are found in 4-3 and World 8-3. They mainly attack by poking their heads out of the holes they're resting in and trying to bite Mario (or Luigi). Some also swim along the path. Unagi can be defeated with a Mega Mushroom and a Super Star. There is also a larger version called the Mega Unagi.
Super Mario Odyssey
Although Unagis don't appear in Super Mario Odyssey, a similar variation called the Maw-Ray does. They attack by swimming out of holes.
Several Unagis reappear in Mario Kart Wii, where they can be seen while traveling through the underwater tunnel in Koopa Cape, poking their heads out of the Pipes underwater. A closer one can be seen swimming outside of Chain Chomp Wheel.
A single one appears in an underwater section of the Mario Kart 8's track Dolphin Shoals, where players race along its body for a short section and can perform Tricks from its undulating body. It returns in the enhanced Nintendo Switch port Mario Kart 8 Deluxe.
Chip Off Whomp's Block • To The Top Of The Fortress • Shoot into the Wild Blue • Red Coins on the Floating Isle • Fall onto the Caged Island • Blast Away the Wall • Switch Star of the Fortress (DS)
Jolly Roger Bay
Plunder in the Sunken Ship • Can the Eel Come Out to Play? • Treasure in the the Ocean Cave • Red Coins on the Ship Afloat • Blast to the Stone Pillar • Through the Jet Stream • Switch Star of the Bay (DS)
Cool, Cool Mountain
Slip Slidin' Away • Lil' Penguin Lost • Big Penguin Race • Frosty Slide for 8 Red Coins • Snowman's Lost His Head • Wall Kicks Will Work (N64)/Mario's Super Wall Kick (DS) • Switch Star of Cool, Cool Mountain (DS)
Big Boo's Haunt
Go on a Ghost Hunt • Ride Big Boo's Merry Go Round • Secret of the Haunted Books • Seek the 8 Red Coins • Big Boo's Balcony • Eye to Eye in the Secret Room • Switch Star of the Basement
Hazy Maze Cave
Swimming Beast in the Cavern • Elevate for 8 Red Coins • Metal-Head Mario Can Move! (N64)/Metal-Head Wario Can Move (DS) • Navigating the Toxic Maze • A-Maze-Ing Emergency Exit • Watch for Rolling Rocks • Underground Switch Star
Lethal Lava Land
Boil the Big Bully • Bully the Bullies • 8-Coin Puzzle with 15 Pieces • Red-Hot Log Rolling • Hot-Foot-it into the Volcano • Elevator Tour In the Volcano (N64)/Inside the Volcano • Flaming Silver Stars (DS)
Shifting Sand Land
In the Talons of the Big Bird • Shining Atop the Pyramid • Inside the Ancient Pyramid • Stand Tall On the Four Pillars • Free Flying For 8 Red Coins (5th Star, N64) (7th Star, DS) • Tox Box Switch Star (DS) • Pyramid Puzzle
Dire, Dire Docks
Board Bowser's Sub • Chests in the Current • Pole-Jumping for Red Coins • Through the Jet Stream • The Manta Ray's Reward (5th Star, N64) (7th Star, DS) • Koopa Surfin' Switch Star (DS) • Collect the Caps... (N64)/Inside the Cage (DS)
Snowman's Big Head • Chill with the Bully • In the Deep Freeze (N64) • Yoshi's Ice Sculpture (DS) • Whirl from the Freezing Pond • Shell Shreddin' for Red Coins (N64) • Snowman's Silver Star (DS) • Into the Igloo • Red Coins in the House (DS)
Shocking Arrow Lifts! • Top o' the Town • Secrets in the Shallows and Sky (N64)/5 Secrets in the Shallows and Sky (DS) • Express Elevator--Hurry Up! • Go to Town for Red Coins (N64)/Go to Town for the Red Coins (DS) • Quick Race Through Downtown! • Soaked Silver Stars (DS)
Tall, Tall Mountain
Scale the Mountain • Mystery of the Monkey Cage • Scary 'Shrooms, Red Coins • Mysterious Mountainside • Breathtaking View from Bridge (Star 5, N64)/Breathtaking View from the Bridge (Star 7, DS) • Blast to the Lonely Mushroom (Star 6, N64) (Star 5, DS) • 5 Secrets of the Mountain
Pluck the Piranha Flower • The Tip Top of the Huge Island • Rematch with Koopa the Quick • Five Itty Bitty Secrets (N64) • Klepto the Condor • Wiggler's Red Coins • Make Wiggler Squirm • Switch Star of the Island (DS)
Tick Tock Clock
Roll into the Cage (N64) • Luigi in the Cage (DS) • The Pit and the Pendulums (N64) • The Pendulum Switch Star (DS) • Get a Hand • Stomp on the Thwomp •Timed Jumps on Moving Bars • Stop Time for Red Coins • Tick Tock Silver Stars
Cruiser Crossing the Rainbow • The Big House in the Sky • Coins Amassed in a Maze • Swingin' in the Breeze • Tricky Triangles! • Somewhere over the Rainbow • Switch Star of the Manor