For a start, I have not been able to find out why we celebrate twelve days of christmas. It is all rather speculative.
The first two significant dates in the life of Jesus are his birthday (which was originally celebrated on at least six different dates, none of which was in December), and the visit to his birthplace by the Three Wise Men, or Three Kings. These dates were fixed as the 25th December - largely to cover up the birthday of Mithras, which was already celebrated on that day - and the 6th of January - known as Epiphany.
You have to shuffle about with the calendar whether you count the 'Twelve Days' from christmas day, in which case the 12th day of christmas is the 5th of January, the Eve of Epiphany, or from Boxing Day, which makes Epiphany the twelfth day.
So Twelfth Night can be either the evening of the 5th or the 6th of January.
There are further complications in that some communities retain the date of christmas as it would be in the old Julian calendar, which makes christmas day either the 6th or 7th of Jan., with Twelfth Night on the 17th, 18th or 19th!
What we mainly know about Twelfth Night is that it was a time of great celebration, feasting and fun. The tradition of celebrating the arrival of the Three Wise Men or Kings is found in many countries. In Spain and France special ring shaped cakes are bakes, stuffed and decorated with preserved fruit. This was carried into Vodu with the festival of Les Rois (the Kings) celebrated on the 6th of January.
In Britain the Twelfth Night Cake was a rich and fruity affair, which also had little trinkets hidden within it. A bean meant that the finder was the King of the night, a pea was for the Queen. But you might find a silver coin symbolising wealth, or a clove which said you were a villain, or a twig for a fool. These were later moved to the christmas pudding instead.
Alcoholic punch, or a drink called Lambswool, was another feature of the celebration, and was served in the Wassail Bowl. Wassail is an Anglo Saxon word, a contraction of wax hael, meaning 'grow healthy' or the equivalent of our modern toast 'Good Health!'
Twelfth Night was also a time when Mummers performed their plays, which usually included the death and resurrection of the hero, symbolising the rebirth of the green world in the Spring. These plays reminded folk that even though it may be dark and cold, Spring will come again.
It has become the tradition that christmas decorations should be taken down by Twelfth Night, although originally they stayed up until Candlemas - the old Celtic festival of Imbolg - 2nd of February.
There are many games which were played during the Twelfth Night party. Perhaps the best known is Snapdragon, where raisins and other preserved fruit have flaming brandy poured over them, and you take turns to snatch the fruit out of the flames. This is not as painful as it sounds, and looks really pretty by candlelight.
There were games involving eggs (which symbolise the new life of the sun, reborn at the Solstice) such as throwing an egg and catching it. The two people moving further apart at each successful catch.
Pass the Slipper was another popular game. All present form a circle, with one in the centre who is blindfolded. Then as music is played, the others pass a slipper one to the next, behind their backs. When the music stops, the one in the middle takes off the blindfold and tries to guess who has the slipper. If they guess right, the one who had the slipper takes their place in the middle and is blindfolded. If there is a large group of revellers, the guesser is allowed three tries.