The Burning of Judas is a folk custom done in various places throughout Greece and other places. It is typically perfomed after the midnight service on Easter Sunday, though sometimes done on Good Friday or Easter Sunday afternoon after the Agape service.
Below is one account of a British tourist to Crete:
The run-up to Cretan Easter in Loutro is a time for the children of the village. For the whole week beforehand they are busily occupied in making an over-life-sized and quite fearsome effigy of Judas. They collect the wood for an enormous bonfire, and burn Judas at the stake on the Saturday night before Easter Sunday. Everyone, locals and visitors alike, gathers round the bonfire as Judas is consumed to the accompaniment of roaring cheers, exploding firecrackers, and the occasional burst of gunfire.
I do not know if this is the custom everywhere: I've only experienced Cretan Easter in Loutro.
Anyway, two years ago I was in Loutro at Easter, staying for the first time in a new studio attached to the Porto Loutro hotel. The lamppost on which Judas was hung was right outside the studio window, so I decided to watch the excitements from my own personal ringside view.
Wow! There was Judas, going up in flames about six feet from my face. I quickly shut the window (which became so hot I was afraid the whole of my little building would be consumed in the conflagratio), and continued to watch in awe as the fire roared and the cinders flew.
It was soon over; Judas dwindled into a pile of ashes to loud cheers from the children, and the bonfire slowly died.
Next day, Easter Sunday, is feast day. Stavros always cooks several lambs and goats on spits behind the hotel, Alison and her friends make a variety of wonderful salads, and everyone who is around is welcome to sit down and partake. The wine and beer flow liberally. Plans for walks that afternoon somehow don't seem so pressing any more...
Here is another account from the ritual in Sifnos:
This custom is sometimes enacted on the evening of Kali Paraskevi (Good Friday) , simultaneously with the bearing of the Epitafios through the streets, though it was observed by this author on the island of Sifnos in 1993, on the Sunday evening after the midday Easter feast, with music following it.
For this ritual, an effigy of Judas Iscariot is fashioned, somewhat like a scarecrow, of old rags stuffed into clothing with a knob-like 'head', the man like figure then affixed to a long pole and borne through the streets by a team of young men. At some point the effigy is set afire and there is a great din of firecrackers, as after (during) the midnight mass (Anastasis).
Though criticized by some as an anti-semitic ritual, and said to be known in some places in Greece as 'The Burning of the Jew', it is possible that those doing the translating of the ritual title are confusing the Greek word for Judas (Ioudhas-pronounced Yoo-dhas), with the Greek word for Jew (Ioudhaios-pronounced Yoo-dhay-ose).
Burning of Judas in Chania, Crete
Burning of Judas in Kalymnos