This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Iku-Turso (Finnish)
Iku-Turso also known as Iku-Tursas, Iki-Tursas, Meritursas, Tursas, Turisas among others) is a malevolent sea monster in Finnish mythology, best known for appearing in the Kalevala. Nowadays Meritursas means octopus in Finnish, named after Iku-Turso, but originally tursas is an old name for walrus while the more common term is mursu.
His appearance remains unclear, but he is described with several epithets: partalainen (the one who lives on the brink, or alternatively, the bearded one), Tuonen harka (the ox of Tuoni, Death), tuhatpaa (thousand-headed), tuhatsarvi (thousand-horned). It was sometimes said that he lived in Pohjola, but that may be because Pohjola was often perceived as the home of all evil.