Tundra Eel is a secret boss in Hard Mode that can be encountered near the rivers that borders Snowdin and Waterfall. He is a Eel monster who is rumored to live in the snowdin rivers and has known to freeze monsters who dare to enter his territory.
He has the appearance of a giant freshwater eel having light silver and white colored scales, white pointy teeth and light blue eyes that shine as bright as the most precious gemstone.
He is extremely territorial and will instantly freeze any trespasser on sight. He is also very egotistical and likes being the centre of attention. He isn't very smart like many other monster, behaving like a primal beast and can only say one or two words at a time.
He is a Ice elemental monster with freezing ice magic. He can shoot a ice energy beam from his mouth, make deadly icicles and summon mini-eels to attack his opponents.
- Tundra Eel's name is actually a anagram of Undertale (much like Deltarune).