This is not in Budapest but very Hungarian. The busójárás. Wikipedia says:
The Busójárás is an annual carnival celebration of the sokci (Croatians) living in the town of Mohács in February. Busójárás lasts six days, usually during February.
Locals originating the Carnival from two similar, but different legends.
According to the more popular legend, during the Turkish occupation of the territory, the people of Mohács fled the town, and moved into the nearby swamps and woods, to avoid Ottoman (Turkish) troops. One night, while sitting and talking around the fire, suddenly an old Sokci man appeared from nowhere, and said the following to them: “Don’t be afraid, your lives will turn to good soon, and you’ll return to your homes. For that time, prepare for the battle, and carve various weapons and scary masks for yourselves, and wait for a stormy night when a masked knight will arrive to you.”, then disappeared the same way, as he come. The refugees followed his order. Some days later, on a stormy night the knight arrived. He ordered them to put up their masks and go back to Mohács, while making as much noise as possible. They followed his lead. The Turks were so frightened from the noise, the masks and the storm in the night, that they thought that eventually demons had attacked them, and ran away from the town before sunrise.
The other, less popular legend is similar to the previous, but in this case, instead of the Turkish army, the winter had been scared away.
Whatever is the truth, the locals are celebrating the Busójárás in early February every year ever since, with “guest Busó teams” from mainly Serbia (local Sokci) and also from Poland.
I saw busójárás often in my childhood because I used to live in Mohács. And though I was very young (3 years old) I remember very well this special event.