L is a fun little category within the Motif Index that stands for Reversals of Fortune. It includes unlikely heroes ("L10. - Victorious youngest son," "L50. - Victorious youngest daughter"), the triumph of the weak over the strong, and poor boys marrying princesses. Also... this:
L315.5.1. Elephant killed by mouse who runs up open end of trunk to head and there smears poison over his brain
In How the Mouse Won His Wife (Congo), a girl is offered as a wife to anyone who can cut down the mahogany tree outside her house. Elephant, Buffalo, Hyena, Leopard, and other large animals all try, but when they stop chopping to take a break, the tree grows back to a whole. Eventually Mouse shows up, gnaws the tree down, and wins the girl.
On the way home with his new wife, Mouse runs into Elephant, who wants to claim the girl for himself. Mouse runs up Elephant's trunk and causes him so much pain that he lets them go, and gives them two pigs. Farther down the road they run into Buffalo who makes the same claim, but Mouse gets into his ear and tortures him until he hands over five sheep. Hyena is next; this time, Mouse calls on a bunch of Squirrels to attack Hyena while he gets away with his wife. After this comes a large Rat; Mouse opens his bag and shows him the head of a dead rat, saying "I have eaten nine rats, you will be the tenth." Rat, very sensibly, runs away. They get home.
One day Leopard shows up at Mouse's house, and tries to run away with the wife. Mouse nonchalantly pulls a Leopard head out of his bag and flashes it, saying "I have killed nine Leopards, you will be the tenth." Leopard is so panicked, he gets into Mouse's calabash, which Mouse puts on the fire, and burns Leopard to death.
Then Mouse says: "I will govern this country, for there is not another chief left."
And if you think this Mouse is hardcore, let me introduce you to Mother Mouse.
In The Mouse's Three Children (Nepal), Mouse has three sons: A Tiger (she prayed for a strong child), a Peacock (she prayed for a beautiful child), and a human Boy (she prayed for a wise, wealthy, and powerful child). The latter gets the King's attention when it turns out that his hair, when cut, turns into pearls and diamonds, and his nails turn into turquoise. The King wants to keep him as a slave, and if the Boy wants to avoid that, he needs to fulfill tasks. The first two are solved with help from Tiger and Peacock, but the last one is different: Mother Mouse has to fight the King's largest bull elephant.
Mother Mouse covers herself in poison, ties a string to her tail, and goes to fight the elephant for her son. She jumps onto the elephant's leg, and then runs up inside of its trunk, and crawls all over its brain, smearing it in poison. When the elephant keels over, the Boy pulls the Mouse out by the string.
Moral of this motif: Never, ever piss off a mouse.
L111.2.3. Future hero found on top of a tree
L111.2.5. Heroine found in harp
L112.11. Heroine born with pigeon’s head
L113.1.3. Mad fisherman as hero
L113.7. Quack-doctor as hero
L114.5. Hero with disgusting habits
L152. Daughter succeeds on quest where son fails
L301. Hermes distributes wit
L311.4. Little innocent girl is able to drive giant out of land
L315.12. Rabbit slays rhinoceros
L391.1. Reed pricks and drives away dog that urinates on it
L419.1. Goose boasts superiority to mushroom
L476. Jackal singing about his deeds falls down from tree and is eaten by alligator
L478. Gnats having overcome lion are in turn killed by spider