You gain a +2 bonus to attack and damage rolls made with this magic weapon and it deals cold damage.
In addition, while attuned to the longbow, when you draw back the string an arrow made of ice magically appears and may be shot*. Also, creatures who take damage from the the longbow lose their reaction for the round. Finally, you also gain cold resistance.
This icy bow was the Pytchsmith's gift to Sadara Mirkyn, Godmother of Blizzards and Balpope of the Elemental Clergy. She awarded it to Froth, Anathema of Gyre and Lifetaker of the Third Sphere, after he won a woeful tournament to wield it.
*This longbow is a homage to the bow wielded by Hank the Ranger from the wonderful Dungeon and Dragons Cartoon from the 1980's.