Whisperknives originated in 3.5 as a halfling prestige class, moved to 4e as a paragon path for rogue, but I felt that the ranger’s magical nature in tandem with favored enemy and the idea that they are the “skirmishers” and “hunters” of the class spectrum made for an interesting ghostly assailant. @JrWarwick gave me the idea for a stealth magic ranger, and this is how the ideas met. Without further ado:
Ranger Archetype: Whisperknife
Whisperknives are a type of ranger that shroud themselves in silence, manipulate illusions, and walk the border of the unseen and are excellent spies, assassins, and bounty hunters. A whisperknife may appear as a vengeful spirit to any hapless witness, silent as the still air, shrouded in mirage, and vanishing in the blink of an eye.
Starting at 3rd level, you learn an additional spell when you reach certain levels in this class, as shown in the Whisperknife Spells table. The spell counts as a ranger spell for you, but it doesn’t count against the number of ranger spells you know.
Your spells are little more than the slightest whisper. At 3rd level, when you cast a ranger spell with verbal components you while you are hidden, any creature that you are hidden from can’t hear you cast the spell. You do not gain this benefit if the spell requires the creature to be able to hear you for the spell to function or if you are wearing armor heavier than light armor.
Additionally you learn the message cantrip. It counts as a ranger spell for you.
Starting at 3rd level, you can imbue your attacks with the bitter essence of silence. Once per turn, you can deal an additional 1d6 psychic damage when you hit a creature with a weapon attack. If you had advantage on the attack roll, you can force the creature to make a Charisma saving throw against your spell save DC. On a failed save, the creature can’t speak or produce any sound until the end of your next turn.
Whisper in the Wind
Beginning at 7th level, you can become as unperceivable as an enemy’s final breath. When you reduce a creature to 0 hit points on your turn, you may immediately use your reaction to become invisible until the end of your next turn or until you make an attack or cast a spell.
From the Shadows
It is often unwise to follow whispers into the dark and your quarry don’t live long to remember that lesson. At 11th level, when a creature within 30 feet of you successfully rolls a Wisdom (Perception) check to detect you while you are hiding, you may use your reaction to move up to half of your speed and make a weapon attack with advantage against that creature. While you are invisible this way, creatures have disadvantage on Wisdom (Perception) checks made to hear you.
You can’t use this feature if you are wearing armor heavier than light armor.
Step of Echoes
As you slay your foes, you walk on the echoes of their last words. At 14th level, when you reduce a creature to 0 hit points during your turn, before the end of your turn you may use a bonus action to teleport to an unoccupied space you can see within 30 feet of you.
Unearthed Arcana Ranger
If you are using the UA Ranger, Whisperknives gain Extra Attack at 5th level.