The Dark Souls series is filled with all kinds of massive boss monsters with some of the most memorable (and horrific) designs in video game history. However, one of the bosses from the original Dark Souls that made a lasting impression on the fanbase had a relatively simple design: Great Grey Wolf Sif was just a big wolf with a sword in its mouth. Despite his very simple look, his boss fight is one of the most infamous sections of the game.
There are a number of wolf-like enemies that appear throughout the early levels of Dungeons & Dragons campaigns, ranging from dire wolves, winter wolves, and even the fearsome werewolves. In Sif's case, the players will be dealing with a huge wolf that eschews the traditional biting & clawing of the other wolves, in favor of gutting party members with the massive greatsword that it keeps clenched in its teeth.
In Dark Souls, Sif is protecting the grave of its former master Artorias, but the player needs to find Artorias' ring, which is required to finish the game. This storyline is easy to fit into a Dungeons & Dragons campaign, as many character classes & spellcasters have loyal animal companions, who could be tasked with protecting something belonging to their master. There are also many well-known real-life stories of animals waiting for their dead masters (like Hachikō in Tokyo), so it's easy to get a cheap reaction out of the players if they are tasked with slaying such a loyal creature.
Setting The Scene
Searching for a grave means that the adventure is more likely to take place outside, which will allow Sif to make the most of its high movement speed. Once the players approach the grave and make themselves known, it will leap into action and slay the interlopers.
The players may have heard rumors of wolves in the woods, but they likely won't be prepared for a giant wolf with a sword in its mouth, nor for the wolf to be swinging the sword in their direction.
Great Grey Wolf Sif's Stat Block
Tactics & Difficulty
A creature as big as Great Grey Wolf Sif will give the melee fighters of the group plenty of room to surround it, but this means they're falling into its trap. Once several warriors have surrounded it, Sif will use its Sword Spin to attack the group, likely causing a lot of damage. This is a recharge move, so it cannot be relied on every turn, but it's sure to give the party members pause and will force them to spread out. Once the party has broken up, Sif is free to launch itself at the spellcasters/ranged fighters and start stabbing.
One tactic that the party members might wanna try which is impossible in Dark Souls is removing the greatsword from Sif's mouth. This should be a herculean task, given the fact that it's one of the few relics remaining of its former master, so the players should at least be given a high STR check at disadvantage of doing it. If the group manages to remove the sword, then switch Sif's attack for the Bite used by a winter wolf until it can reclaim the weapon. On its own, the sword is simply a well-made greatsword, with the radiant damage being the result of Sif's own powers, instead of magic in the weapon.
It's unusual for modern video games to have urban legends regarding their content, considering how easy it is to confirm or deny whether a rumor is real. Dark Souls is a rare example of this, as there were persistent rumors that there was a way to spare Sif, but these turned out to be untrue, and the conflict only ends in bloodshed. The DM is free to tell whatever story they wish, however, and it's possible that they can offer an alternate ending to Sif's story. Maybe the players can somehow placate Sif, or use magic to communicate with it and convince it to step down. It's also possible that they could steal whatever item they need and escape before it can catch up, forcing it to return to the grave in a more paranoid state. The Sif battle in Dark Souls is one of the saddest moments in the series, and that might not be the kind of story that DMs want to use in their game, so they should be open to changing the end of Sif's tale in Dungeons & Dragons.