Magic based on certain sounds the human mouth can produce. Or in other words, magic via beat-boxing.
A bullied child goes into secret intensive training for a month to try and take down his bully. When he gets back, the bully still wipes the floor with him. This happens three times before the poor kid spies on the bully and realizes that, every month, the bully does intensive secret training just to stay on top.
An army of 1,000 waits atop a valley to face off against enemy forces. To their surprise, soldiers don’t come charging over the opposite hill; they instead face 10,000 armored bears.
Magical power is directly correlated to beard gloriousness. Glorious beards can be shaved from defeated wizards, fashioned into staves and wands, and sold to people without beards.
Your protagonist lives in a painting and communicates with people outside the paintings by being meaningful.
Many fantasy heroes are called to action by some kind of animal. Your animal is a chocolate chip dog.
Legends say arrows can’t kill your protagonist, so s/he gets sent into archer-heavy areas. S/he successfully takes out thousands of archers single-handedly until the twist happens: arrows actually can kill this legendary arrow sponge — archers just have to learn how to aim.
The protagonist is a gardener who doesn’t have a clue how to swing a sword, shoot a bow, or cast spells. S/he instead gardens the evil overlord to death.
Your protagonist finds a way to non-violently end the evil overlord’s reign: shrinking him to the size of a small chipmunk. The hero returns home, only to find that, a week later, the evil overlord is still ruling the land, using a voice changer and illusion magic to fool everyone into thinking he’s the same size.
A magic system that can only be used by camels and penguins. Humans and other sentient races, if your world has them, can fight for control over these legendary animals, who likely have their own agenda.