What is the name of the large horned beast Din Djarin fights in Season 1? It is a mudhorn.
The mudhorn appears in "Chapter 2: The Child," after Jawas strip parts from the Mandalorian's ship, the Razor Crest. To recover those parts, Din must retrieve the egg of the dangerous creature living on Arvala-7. The mudhorn attacks him in a muddy cavern, where his blaster, flamethrower, and other weapons fail to stop it.
Din is badly battered and nearly killed until Grogu uses the Force to lift the charging beast. That brief intervention gives Din the opening to stab the mudhorn in the neck. He returns the egg to the Jawas, who cut it open and eat its contents, allowing him to regain the stolen ship parts.
The creature is often confused with a bantha, dewback, or rancor, but those are different Star Wars animals. The mudhorn becomes especially important later: the Armorer places its image on Din's armor as his signet, symbolizing the bond between Din and Grogu.