He often allied himself with noble Knights to fight against other princes or against the cities, whose burgeoning power was anathema to him.

In July, the citizens under captain Moritz von Uslar defeated him in a pitched battle between Rosdorf and Grone.

After he was expelled from Göttingen, Otto had to reside in Hardegsen, where he had acquired Hardeg Castle in 1379 from the Lords of Rosdorf.

By this time, he had been excommunicated, which is why he was buried in unhallowed ground north of the church of Wiebrechtshausen monastery at Northeim.

The final verdict on Otto I is negative, because he overestimated his powers and left himself weakened when he fought too many fights at once.

They had two children, a son, Otto II, who succeeded his father, and a daughter, Elisabeth, who married Eric I, Duke of Brunswick-Grubenhagen.