Vecna has become one of the most famous Dungeons & Dragons villains of all time, thanks to his name-alike appearing in Stranger Things. The D&D 5e groups who want to use Vecna in their campaigns can now do so, as Wizards of the Coast released a free PDF that stats him out and offers information about his history and motivations. Vecna has always been a popular D&D villains, as Hand and Eye of Vecna offer incredible power to parties, so long as they don't mind missing a limb and losing their souls.
Vecna originated from the world of Oerth in the Greyhawk campaign setting, which is one of the oldest D&D settings in the history of the game. He started out as a powerful mortal spellcaster, who transformed into an undead lich, before having his plans for godhood thwarted by his traitor lieutenant, who cut out Vecna's eye and sliced off his hand. The loss of these body parts only acted as a temporary roadblock for Vecna, as he eventually became a demigod, and is currently a full deity, acting as the god of secrets in the world of Oerth. Vecna's name is also known in the other D&D campaign settings, thanks to missing limbs causing havoc whenever they appear.
In the current timeline of the D&D multiverse, Vecna is a major deity and is unlikely to face parties head-on. D&D groups can face the cult of Vecna, as they will provide a challenging threat to the party, rather than the overwhelming wrath of a god. There is a version of Vecna in D&D 5e that can be faced by the party, as Wizards of the Coast wrote statistics for an earlier version of the character, before he lost his hand and eye, and before he ascended to godhood. This version of Vecna is included as part of the Vecna Dossier and players can download it for free, so long as they don't mind registering to D&D Beyond.
Vecna Can Be Added To D&D 5e Using The Free Vecna Dossier
The people who register to D&D Beyond can download the Vecna Dossier, and this version of Vecna is a D&D Challenge Rating 26 creature, which means that only the most powerful of groups will be able to face him a fair fight. The DM doesn't necessarily need to make the fight fair, as some adventures will include incredibly powerful foes, but DMs will likely give the players a special bonus or weapon that lets them tip the scales in such battles. One example of this involves Vecna himself, as his avatar appears as a foe in the Vecna Lives! 2e campaign, but players are aided by Iuz: a powerful evil demigod who matches Vecna in strength. The two do battle while the players need to take on Vecna's cultists and rob him of their support.
Vecna is suited for use as the end boss for a long-running campaign. The Vecna Dossier presents an older version of the character, so he would fit in a campaign set in an ancient version of Oerth. It's also possible that the CR 26 version of Vecna can be used as a stand-in for his avatar, which could appear in any setting, as Vecna ended an entire D&D edition and has a habit of plane-hopping, trying to extend his reach across the multiverse. There are lots of possibilities for using Vecna in a Dungeons & Dragons campaign, so long as the DM is fine with a TPK.
Source: D&D Beyond