Great Grey Wolf Sif

Great Grey Wolf Sif is a boss in Dark Souls.

Location
Sif can be found in Darkroot Garden behind large, glowing doors, guarding the grave of Artorias the Abysswalker, one of Gwyn's four knights.

Artorias of The Abyss
Sif makes an appearance in the Artorias of The Abyss DLC. The player finds the wolf located behind an Illusory Wall after being led about by Alvina in the Chasm of the Abyss. Sif is found protected by a magical barrier, which was created by Artorias using his Greatshield in order to shield the wolf from the corruption of the Abyss. Upon reaching him after defeating the Humanity Phantoms, Sif will vanish and leave behind Artorias' shield. As long as Sif was rescued by the player, he can be summoned during the battle against Manus, Father of the Abyss.

If the Chosen Undead saves Sif in the Chasm of the Abyss before killing Sif in Darkroot Garden, a different cutscene will play before the fight; however, this can only be done if the player places the Lordvessel in the altar through Firelink Shrine, as Artorias' ring is needed to access Kaathe. In the cutscene, Sif will recognize the player as they approach and let out a whimper. The protagonist reaches out to pet the wolf, but Sif pulls away and howls mournfully before sadly picking up Artorias' greatsword. The fight will continue as normal after this point.

Strategies
Getting underneath Sif so that the player is out of reach is a reliable strategy, but the player is still susceptible to Sif's slam attack while in this position.

Using sorcery or pyromancy to soften Sif up before moving in with melee attacks can also prove to be effective.

Using a summoned phantom as a decoy can make positioning oneself under the wolf easier.

Sif's attacks can be blocked, but many will cause massive stamina damage. Learning Sif's moveset patterns is wise to survive the fight.

Dashing Slice
Like all of Sif's attacks, this can be blocked. However, this attack hits twice; once with the sword, and again if Sif's body touches the player. If the player blocks both, massive stamina damage is guaranteed.

Spinning Slice
Sif repositions the sword to a straight position, and spins around twice. Causes massive stamina damage if blocked and can kill players if the slices connect. Can be dodged by backing or rolling away before the attack is unleashed. Sif will pause afterwards, creating an opportunity for attack.

Sword Slam
Sif slams the sword into the ground. Powerful, but has no tracking and poor hitbox. Attack is blockable, has no follow up attacks and has substantial recovery.

Evasive Slice
Sif will attempt to slice the player while jumping backwards and away from the player in one motion. Has little to no starting lag. Blocking it won't give the player an opportunity to attack, but will help the player survive.

Single Slice
Sif will do a quick chop from side to side. Good tracking and high hitbox. Possible to roll underneath it with good timing. Also does not do much damage to the stamina bar, thus it can be blocked quite easily.

Double Slice
Two slashes from side to side. Great tracking, thus very difficult to sidestep. However, the slices can be rolled under and blocked fairly comfortably without the stamina bar being fully drained.

Finishing Combo
Sif will slice twice and then finish with an overhead smash. The last attack has poor tracking and a small hitbox, so use this as an opportunity to get some hits in.