The Dawn's Darkness is a Crimson only equivalent to the Night's Edge, added by the N Terraria mod. It, unlike its sibling sword, can only be crafted with the Blood Butcherer and the other three swords involved in a Night's Edge at demon altars. Like its sibling sword, it can be crafted into a True version of itself with a Broken Hero's Sword, and later into the Terra Blade. It still can only be crafted on a Bloody (crimson) world, however.
The Stats of the Dawn's Darkness are Equal of the Adamantite Sword. Making it a Perfect Early hardmode Weapon.
The Dawn's Darkness functions similarly to Vampire Knives, restoring health on successful hits. This comes in handy when combined with damage multiplying effects like Heavy Slash or against worm type enemies, where it can hit multiple times.