Wikia

Sloth Monster

Biographical information
Aliases	Lethargo
Affiliation	Thirteen Monsters
Physical description
Out of universe information
Era(s)	Fourth movie
Teachers and Students

[Source]

The Sloth Monster is one of the Thirteen Monsters that appears in TMNT (2007 film). It is likely based on the Mapinguari, a sloth-like cryptid that has been reported as living in the Amazon rainforests.

In the book The Legend of Yaotl, it is called "Lethargo".