My favourite fairytale, mostly for its oddness, is The Snake Who Became The King's Son-In-Law or as I call it, 'Herp: The Snake Who Was His Own Boostrap'.
Here it is in its entirety, taken from sacred-texts.com:
No. 7.--The Snake who became the King's Son-in-law
There were an old man and an old woman. From their youth up to their old age they had never had any children (lit. 'made any children of their bones'). So the old woman was always scolding with the old man--what can they do, for there they are old, old people? The old woman said, 'Who will look after us when we grow older still?'
'Well, what am I to do, old woman?'
'Go you, old man, and find a son for us.'
So the old man arose in the morning, and took his axe in his hand, and departed and journeyed till mid-day, and came into a forest, and sought three days and found nothing. Then the old man could do no more for hunger. He set out to return home. So as he was coming back, he found a little snake and put it in a handkerchief, and carried it home. And he brought up the snake on sweet milk. The snake grew a week and two days, and he put it in a jar. The time came when the snake grew as big as the jar. The snake talked with his father, 'My time has come to marry me. Go, father, to the king, and ask his daughter for me.'
When the old man heard that the snake wants the king's daughter, he smote himself with his hands. 'Woe is me, darling! How can I go to the king? For the king will kill me.'
What said he? 'Go, father, and fear not. For what he wants of you, that will I give him.'
The old man went to the king. 'All hail, O king!'
'Thank you, old man.'
'King, I am come to form an alliance by marriage.'
'An alliance by marriage!' said the king. 'You are a peasant, and I am a king.'
'That matters not, O king. If you will give me your daughter, I will give you whatever you want.'
What said the king? 'Old man, if that be so, see this great forest. Fell it all, and make it a level field; and plough it for me, and break up all the earth; and sow it with millet by to-morrow. And mark well what I tell you: you must bring me a cake made with sweet milk. Then will I give you the maiden.'
Said the old man, 'All right, O king.'
The old man went weeping to the snake. When the snake saw his father weeping he said, 'Why weepest thou, father?'
'How should I not weep, darling? For see what the king said, that I must fell this great forest, and sow millet; and it must grow up by to-morrow, and be ripe. And I must make a cake with sweet milk and give it him. Then he will give me his daughter.'
What said the snake? 'Father, don't fear for that, for I will do what you have told me.'
The old man: 'All right, darling, if you can manage it.'
The old man went off to bed.
What did the snake? He arose and made the forest a level plain, and sowed millet, and thought and thought, and it was grown up by daybreak. When the old man got up, he finds a sack of millet, and he made a cake with sweet milk. The old man took the cake and went to the king.
'Here, O king, I have done your bidding.'
When the king saw that, he marvelled. 'My old fellow, hearken to me. I have one thing more for you to do. Make me a golden bridge from my palace to your house, and let golden apple-trees and pear-trees grow on the side of this bridge. Then will I give you my daughter.'
When the old man heard that, he began to weep, and went home.
What said the snake? 'Why weepest thou, father?'
The old man said, 'I am weeping, darling, for the miseries which God sends me. The king wants a golden bridge from his palace to our house, and apple and pear-trees on the side of this bridge.'
The snake said, 'Fear not, father, for I will do as the king said.' Then the snake thought and thought, and the golden bridge was made as the king had said. The snake did that in the night-time. The king arose at midnight; he thought the sun was at meat [i.e. it was noon]. He scolded the servants for not having called him in the morning.
The servants said, 'King, it is night, not day'; and, seeing that, the king marvelled.
In the morning the old man came. 'Good-day, father-in-law.'
'Thank you, father-in-law. Go, father-in-law, and bring your son, that we may hold the wedding.'
He, when he went, said, 'Hearken, what says the king? You are to go there for the king to see you.'
What said the snake? 'My father, if that be so, fetch the cart, and put in the horses, and I will get into it to go to the king.'
No sooner said, no sooner done. He got into the cart and drove to the king. When the king saw him, he trembled with all his lords. One lord older than the rest, said, 'Fly not, O king, it were not well of you. For he did what you told him; and shall not you do what you promised? He will kill us all. Give him your daughter, and hold the marriage as you promised.'
What said the king? 'My old man, here is the maiden whom you demand. Take her to you.'
And he gave him also a house by itself for her to live in with her husband. She, the bride, trembled at him.
The snake said, 'Fear not, my wife, for I am no snake as you see me. Behold me as I am.'
He turned a somersault, and became a golden youth, in armour clad; he had but to wish to get anything. The maiden, when she saw that, took him in her arms and kissed him, and said, 'Live, my king, many years. I thought you would eat me.'
The king sent a man to see how it fares with his daughter. When the king's servant came, what does he see? The maiden fairer, lovelier than before. He went back to the king. 'O king, your daughter is safe and sound.'
'As God wills with her,' said the king. Then he called many people and held the marriage; and they kept it up three days and three nights, and the marriage was consummated. And I came away and told the story.
Cf. Hahn's No. 31, 'Schlangenkind' (i. 212) and notes, but the stories are not identical; and his No. Too, especially the note (ii. 313) for Indian version. Wratislaw's Croatian story, No. 54, 'The Wonder-working Lock,' p. 284 (see under No. 54), offers striking analogies. Cf. too for cobra palace, Mary Frere's Old Deccan Days, p. 21.
Image from here.