Winter Knight's Mantle

The Winter Knight's Mantle is the power, or Mantle, bestowed upon the Winter Knight by the Winter Queen.

Description
Winter Knight's Mantle is the power passed on by the Winter Queen to a chosen mortal to make them the Winter Knight.

Features

 * Harry describes it as a "cold, clear power".
 * The Winter Knight is a weapon useful to the Winter Queen but it is one with two edges. The Winter in the Knight comes from the Queen and she is just as vulnerable to the Knight as any other Sidhe.
 * Any metal that gets into the knight's skin disrupts the mantle's power, weakening the knight.
 * Increased Pain Threshold: Butters' theory is that Mab fiddled with the pain threshold so that her knight can plow through her enemies without stopping even for knife wounds.

Character changes

 * The changes to the bearer start with strong impulses and intense emotions and then builds and doesn't stop.

Harry Dresden's new abilites

 * Ice Enhanced Spells: Winter Court power in his spells using ice in various manifestations.
 * Strength and Speed: Harry ran faster when he should gotten tired in the FBI HQ toward the Way, even faster than Susan. Harry cracked the sternum of a half-vampire with a kick.
 * Heightened Vision
 * Mab's Voice: gave Harry a protection of frost as he started to weary and slow down on the stairs of the Temple of Kukulkan reviving him with renewed energy and strength.

Harry Dresden's spells

 * Arctis: froze Stevie D's gun.
 * Infriga: froze 3 Chichén Itzá vampires ablaze from Harry's first spell, a bullet shattered them.  Harry used it dueling Arianna Ortega at Chichén Itzá in combination with Forzare killing her with spears of ice.
 * Wind and Ice: Harry unleashed a burst of freezing wind, later blankets the field with ice and howling wind while fighting the Jaguar Warriors in the Ball Court at Chichén Itzá (no spell word named).
 * Rexus Mundus: a globe of blinding blue light creates an iceburg from absolute zero cold plunging into water.

In the series
In Summer Knight (novel), after capturing the traitor Lloyd Slate the current Winter Knight, Mab asked Harry to take up the Winter Knight's Mantle and all of he debts to her would be cancelled. He refused.

In Dead Beat, Mab stops answering his questions about Die Lied der Erlking and the Heirs of Kemmler because she will not give information for free. For the second time Mab asks Harry to take up the Mantle—she will cancel his debts and answer all of his questions freely. Once again, Harry refuses.

In Small Favor, Mab charges Harry with his second task for her, to find Marcone who had been abducted. And for the third time she asks him to take up the Winter Knight's Mantle, and again Harry refuses.

In Changes, desperate, having just broken his back and unable to save his daughter from the Red Court vampires who abducted Maggie for a ritual Bloodline curse sacrifice in Chichen Itza, Harry summons Mab and bargains to take the Winter Knight's Mantle for the power and strength and restored health of his body and the time to save Maggie. They make a deal and to seal it, Harry had to sacrifice Lloyd Slate on the Stone Table with Medea’s Bodkin.

In Cold Days, Bob explains to Harry that it doesn't makes sense that Mab would want Maeve killed since the Mantle would simply pass on to another who would become another "Maeve" since the Mantle changes that person who wears it. Thomas advised Harry not to ignore the predatory impulses of the Mantle, to acknowledge them instead to as to be in control of them and not let them sneak up on him.

The instant that Harry said: "So, screw Winter Law—", the Mantle disappeared. Harry was filled with intense pain and fatigue, followed by his body going completely numb from the waist down. He could no longer hold himself up or have any control over the functions of his lower body, due to the broken back he had suffered before taking up the Mantle. So, not only was the Winter Knight's power taken away but his body was returned to the state it was in prior to taking on the Mantle. It came back a moment later.

The power of the Winter Knight's Mantle restored Harry Dresden's shattered body, and gave him strength, speed, endurance to the limits of human ability, and possibly more, so long as Harry obeys Winter Law.