Stalker

""Some have walked these desolate worlds while you have slept. Some like me. I remember what you did. I remember the day.

The Tenno appeared at the Terminus, gleaming and victorious. Our cold and gold Emperors, breathless, bathed you in savior's silk. Then came the sound. Across all our worlds, all at once, the ceremonial Naga drums. A royal salute to the honored Tenno. Ten solemn beats to declare the suffering was over. I watched from a distance, with the rest of the low Guardians. With each beat terror began to crush my throat. The Tenno were not stoic and silent. They were waiting. They were poised. I tried to call out but only a strangled whisper escaped.

When the ninth beat rang a torrent of blood filled the stadium, loosed by Tenno blades. The drums, the Empire, fell silent forever.

Now I hunt, dividing your numbers. Watching from that dark place, cataloging your sins, I am the ghost of retribution. You may forget but you are not innocent.""

- Stalker's Codex Description

The Stalker is an ominous, vengeful figure that infrequently appears during missions, encountered with a level that ranges anywhere between 15 to 80, that will target and attack a single player within the current cell.

This entity will taunt the player with messages, similar to bosses. For the duration of these messages, the targeted player's HUD will flicker, along with any surrounding lights. After three taunts, the Stalker will appear in black smoke and proceed to attack the targeted player.

The Stalker's current arsenal is comprised of a bow known as the Dread, a scythe called Hate, throwing knives known as Despair, and an unknown Warframe that is capable of using abilities from various Warframes -- save for his Dispel.

If the targeted player is dead, the Stalker will disappear in a cloud of black smoke. If the Stalker is forced to flee (by damaging him up to 90%), a bounty of blueprints and more can be obtained.

In General
The Stalker attacks with high damage output which can kill an inexperienced player with few attacks. The obvious strategy is to keep moving to avoid his arrows and abilities. The Stalker targets only one player at a time, it is a good idea to hide and let your teammate(s) (if any) assault him. If the target player chose to run away, the Stalker will occasionally teleport melee the player, like a Grineer Flameblade.

When in a moderately long range, the Stalker will occasionally use Slash Dash at his target. Avoid getting hit at all cost as it is lethal (around 1,200 damage).

The Stalker is factionless, and so he will be attacked by all factions regardless of Tenno's prescence. A good idea would be to lure him into a room full of enemies and let them do the job for you.

Shotguns appear to be effective, especially with Armor Piercing and/or Shock damage. Given the Stalker's favor of melee combat and agility, it can be hard to land anything besides shotgun blasts.

Utilizing Warframe Abilities
True to his taunt: "Your TENNO powers are useless", the Stalker will ignore all support abilities (including Sentinels') such as Chaos and Snow Globe and is able to purge buffs like Iron Skin and Blessing with his ability, Dispel. Offensive abilities will damage the Stalker, but not apply additonal effect that comes with it (e.g., Rhino Stomp will damage, but not suspend him).

Mag's Shield Polarize and Trinity's Blessing will charge the squad's shields when in need (and health in Trinity's case), this is a beneficial ability as an unexpected move from the Stalker can be lethal.

As of Update 10.7, he is also immune to Frost's Snow Globe while inside, also said above that he can dispel it.

When low on health, the Stalker will sometimes cast what resembles Nyx's Absorb with no visual effects. Attackers within the blast range will receive damage from it, cease fire and run away when he activates Absorb.

Other Resolutions
If the victims wish to keep themselves from harm, they can avoid the Stalker when he spawns by maintaining a long distance about 50 meters or more apart between him, as the 50 meters is considered to be the ability limit for all Warframes, this would mean the Stalker as well. The Stalker is still capable of teleporting to you rather than pulling you towards it.

Victims can escape the Stalker's attacks entirely by completing missions accordingly and quickly, in order to minimize the intrusions provided by the Stalker. This would mean for the players not to receive his drops in the process, but spares revives effectively.

Quotes
Stalker's list of taunts (one randomly chosen 3 times in the following order):

Taunt 1 Taunt 2 Taunt 3  Player Defeated   Stalker Defeated  Misc
 * (Player's name), you can't run from your past.
 * (Player's name) there is no place to hide.
 * I know your every move (player's name).
 * The blood of (boss' name) is on your hands. Did you really think there would be no repercussions?
 * The murder of (boss' name) will not go unpunished.
 * There is no salvation for your crime against (boss' name).
 * You shall not leave this place!
 * I am your reckoning!
 * Your sentence is death!
 * (Player's name) shall not trouble us again.
 * It is done. (Player's name) is no more.
 * Justice is served. (Player's name) has been executed.
 * What have you...done?
 * No?! This is not... possible.
 * I have failed. (Player's name) lives.
 * I... have failed... this one will remain... unpunished...
 * Your TENNO powers are useless!

Trivia

 * The Stalker appears to be wearing a dark-colored Excalibur suit with a unique helmet.
 * It has been noted that the Stalker will rarely exhibit much higher intelligence, preforming wall runs, dive rolls, tracking cloaked players, and even actively avoiding enemies and other Tenno. It is unknown if this is due to certain rooms being designed for his AI, or reasons unknown.
 * As of Update 10.5.0, the Stalker has a new ability called Dispel.
 * The Stalker will toss his Despair in the air when in an unalerted status (usually caused by a bug).
 * If ever the Stalker appears and disappears in one of the victim's missions, his Combat Music will replace the conventional Combat Music for the rest of the mission.
 * The Stalker seems to spawn from inside of the cryopod in defense missions if the user who he is targeting is somewhat near it or ontop of the pod.

Bugs

 * On rare occasions, the Stalker will glitch when he uses his cloaking ability, becoming permanently invincible to damage dealt by your team, being only damaged by enemies. This seems to be associated with the bug below as well.
 * Rarely, the Stalker can spawn in a defense mission but replace the pod health bar with his own health. Even if the pod were to be destroyed as long as the Stalker remains alive, the mission continues. The Stalker then proceeds to attacking enemies by itself. Once the Stalker gets downed, he can be revived normally just like a downed teammate.
 * When the Stalker is killed during a mission, the mission complete music is replaced with the Stalker theme. Same thing happens to the defense music, you will continuously hear the Stalker music during a wave. After finishing the planet it will return to the normal music.
 * There is a rare bug where the Stalker will be named after the respective boss of the area in his health meter. (i.e Tyl Regor on Titania, Uranus, or Kela De Thaym on Merrow, Sedna). (Needs Confirmation)
 * There have been occasional encounters with level 1 Stalkers, perhaps due to host/client lag or glitches.
 * If the targeted Tenno is downed already before the Stalker spawned, the Stalker will freeze and become invincible.
 * The Stalker can appear in the Tutorial (if played again by more veteran players)
 * The Stalker can appear in the Mastery Rank tests.
 * Stalker will become permanently invulnerable after using his Absorb ability.

Media
The Stalker's voice used when taunting players.