Mega Unagi

From the Super Mario Wiki

A Mega Unagi..

Mega Unagis are a gigantic sub-species of the Unagi that appeared in New Super Mario Bros. Mega Unagis chased Mario (or Luigi) through two underwater stages in the game, trying to eat him. They were very dangerous, and ate everything they could, such as bricks and ? Blocks. There was no way to defeat a Mega Unagi. However, Mario could go through him with a Mega Mushroom.

New Super Mario Bros.

Protagonists	Mario \| Luigi \| Princess Peach \| Toadsworth
Worlds	World 1 \| World 2 \| World 3 \| World 4 \| World 5 \| World 6 \| World 7 \| World 8
Bosses	Bowser Jr. \| Bowser \| Mummipokey \| Cheepskipper \| Mega Goomba \| Petey Piranha \| Monty Tank \| Lakithunder \| Dry Bowser
Items	Super Mushroom \| 1-Up Mushroom \| Mini Mushroom \| Mega Mushroom \| Fire Flower \| Blue Shell \| Star \| Coin \| Silver Coin \| Red Coin \| Red Ring \| Big Star
Enemies	Balloon Boo \| Banzai Bill \| Blockhopper \| Bob-omb \| Boomerang Bro. \| Boo \| Broozer \| Bullet Bill \| Buzzy Beetle \| Chain Chomp \| Cheep-Cheep \| Cheep-Chomp \| Deep-Cheep \| Dry Bones \| Fire Bro. \| Fire Chomp \| Fire Snake \| Goomba \| Hammer Bro. \| Kab-omb \| Koopa Paratroopa \| Koopa Troopa \| Lakitu \| Mega Cheep-Cheep \| Mega Deep-Cheep \| Mega Unagi \| Micro-Goomba \| Moneybags \| Paragoomba \| Piranha Plant \| Podoboo \| Pokey \| Scuttle Bug \| Skeeter \| Snailicorn \| Snow Spike \| Spiny \| Splunkin \| Squiggler \| Super-Whomp \| Super Dry Bones \| Super Piranha Plant \| Super Thwomp \| Sushi \| Sumo Bro. \| Swooper \| Thwomp \| Unagi \| Venus Fire Trap \| Wiggler