Loki

"Don't think you can just fly off and never return," said Thor, and he stroked his white beard meaningfully. "I may be old now," he said, "but if you do not return, ancient as I am, I will hunt you down, wherever you hide, and I and my hammer will be your death. For I am still Thor! And I am still strong!"
"You are still extremely irritating," said Loki. "Save your breath, and you can use your strength in making a pile of wood shavings beyond the walls of Asgard. An enormous pile of wood shavings. You will need to cut down many trees and chip them into thin shavings. I'll need a long high pile, atop the wall, so you should start now."
Then Loki wrapped the falcon cloak tightly about himself and, in falcon form, flapped his wings and rose, faster even than an eagle, and was gone, flying north, towards the lands of the frost giants.

[...]

Thiazi saw a falcon's feather on the ground, and he knew in that moment whee Idunn was and who had taken her.
He leapt into the sky in the form of an eagle even huger and mightier than any he had been before, and he began to beat his wings and flew, faster and ever faster, towards Asgard.
The world moved beneath him. The wind blew about him. He went even faster, so fast that the air itself boomed with the sound of his passing.

[...]

When he spooted a falcon ahead of him, Thiazi let out a scream of rage and increased his speed.
The gods of Asgard heard the screech and the boom of the wings, and they went to the high walls to see what was happening. They saw the little falcon coming towards them, the enormous eagle so close behind it. The falcon was so close . . .
"Now?" asked Thor.
"Now," said Freya.
Thor set fire to the wood shavings. There was a moment before they caught—a moment just long enough for the falcon to fly over them and to settle inside the castle, and then, with a whoomph, they burst into flame. It was like an eruption, a gout of fire higher than the walls of Asgard itself: terrifying, and unimaginably hot.
Thizai in eagle form could not stop himself, could not slow his flight, could not change direction. He flew into the flames. The giant's feathers caught fire, the tips of his wings burned, and, a featherless eagle, he fell from the air and crashed to the ground with a bang and a thud that shook the fortress of the gods.
Burned, dazed, stunned, the naked eagle was no match even for the elderly gods. Before he could transform himnself back into giant shape he was already wounded, and as he changed from bird into giant, a blow of Thor's hammer parted Thiazi from his life.