Mszczuj of Skrzynno (; also Mà Âciwoj of Skrzynno; Polish: Mszczuj ze Skrzynna; died in 1446) was a Polish knight who served under Wà Âadysà Âaw Jagieà Âà Âo and participated in the Battle of Grunwald on 15 July 1410 against the Teutonic Knights. He was a knight in the royal household regiment of the King of Poland (cubiculariorum) and bore the à ÂabÃÂdà º (Swan) coat of arms.
According to the Polish chronicler Jan Dà Âugosz, Mszczuj was part of the third Rota, a unit of cavalry of the royal household under the leadership of Andrzej Cioà Âek of à »elechowo and Jan OdrowÃ à ¼ of Sprowa. Dà Âugosz reports that Mszczuj was the knight who defeated and killed the Grand Master of the Order, Ulrich von Jungingen, during the Battle of Grunwald. Dà Âugosz offers two pieces of evidence for this. First, Mszczuj's squire, Jurga, acquired and handed over a valuable reliquary with holy relics that had previously belonged to von Jungingen, as well as the Grand Master's battle cloak. Second, the location of the Grand Master's body was made possible thanks to directions given by Mszczuj, indicating that the two knights had definitely engaged each other on the battlefield.
On 10 September 1410, Mszczuj took part in a follow-up battle against the Teutonic Knights at Koronowo, contributing to the Polish-Lithuanian victory.
In 1412, he was part of the delegation and personal escort of Wà Âadysà Âaw Jagieà Âà Âo to the Kingdom of Hungary, where he participated in tournaments and jousts. In 1428, he took part in the expedition against Great Novgorod led by the Grand Duke of Lithuania Vytautas. In 1431, he participated in Wà Âadysà Âaw Jagieà Âà Âo's campaign against the rebel à  vitrigaila in Lithuania and was present at the siege of Lutsk. A year later, he led reinforcements for the new Grand Duke, Zygmunt Kiejstutowicz, in his war against à  vitrigaila.
Mszczuj owned large tracts of land in Volodymyr. A 15th-century church, purportedly built by Mszczuj, can be found and visited in Opoczno.