Deck of Many Things

The Deck of Many Things is a legendary wondrous item. Usually found in a box or pouch, this deck contains a number of cards made of ivory or vellum. As soon as a character draws a card from the deck, its magic immediately takes effect. Each card has a different effect: either amazing and great or immensely destructive. The cards are split about 50/50 between good and awful, and it is widely regarded as one of the most powerful artifacts in Dungeons & Dragons. As Liam put it, "you could destroy the world".

Discovery
While looting the lair of Thordak beneath Emon, Grog began searching for "unique-looking knick-knacks or really lovely/dangerous-looking weapons." One of the items he found was a beautifully engraved wooden box. After prying it open by breaking it in half, a small leather sleeve fell out. Grog opened the sleeve and saw about thirteen tarot cards. Before Grog could throw the deck into nearby lava, Vex came over and told him to hold onto it until she had time to look around for other cool stuff.

The First Pull
Intrigued by the cards, Grog pulled one from the middle of the deck. Travis drew the Queen of Spades, which Matt misread as "Key". Thus, Grog was awarded a rare magic weapon: a Dancing Sword.

Grog tried to stealthily pocket the remaining twelve cards, but he failed with a Natural 1. Grog almost threw them, and Vex picked up the deck. Being a studious child, Percy had read myths and legends about glory and woe all revolving around the Deck of Many Things. Before Vex could pull a card (tempted by Grog's explanation that they create weapons), Percy warned her not to draw and to be very careful: those cards could make a lot of bad things. Vex closed the case and stuffed it in her shirt.

The First Pull (corrected)
While Grog was showing off his new sword to Kerrek, Grog suddenly felt a bursting headache at the back of his mind. Looking at the blade, Grog saw a medusa-like visage image begin to seep through the metallic sheen (Grog assumed it to be the sword's "female setting"). As Grog fell to his knees, clutching the sides of his head, the sword clacked to the ground and almost immediately rusted and turned dark and dull.

This was Matt retconning his mistake from the previous episode, as the card drawn by Grog was actually "Euryale". Thus, Grog was cursed by the Dancing Sword and after the curse was expended, Grog took a permanent -2 penalty on saving throws until a god ends the curse.

Grog tried to trade the Periapt of Wound Closure to Vex in order to get his deck back, but Vex tricked him by giving him a leather pouch with rocks inside. Vex made Grog promise not to pull anything from it: he could only keep it in its little pouch.

After Scanlan left, Vex discovered Scanlan had been using drugs. Feeling guilty for also having kept something serious from everyone else, Vex confessed to Grog and gave him back the Deck of Many Things. Grog was confused, and believed that he had always had the deck and Vex was apologizing to him for some weird reason.

The Second Pull
During his year off in Vasselheim, Grog got curious again about the Deck of Many Things. After a lot of drinking and fighting, Grog simply ran out of stuff to keep himself entertained. However, remembering Vex's warnings, he found a nice drunk sap in the Quadroads. After confirming that the drunk didn't know what the deck was, Grog offered him a card. Believing it to be some sort of magic trick, the drunk drew a card: "Moon". The drunk was granted two wishes (1d3 Wish spells), immediately using the first to wish to be "a powerful lord of the Quadroads". The Lord of the Quadroads thanked Grog, who introduced himself as "Grog Strongjaw, Maker of Kings". The Lord of the Quadroads proudly declared that he still had one wish left, and ran off to his waiting carriage. Grog shouted after him, asking what his name was,

Grog's first instinct was to pull all the cards right then in that moment. However, he decided to wait until he could open it with his good friend, Pike. Besides, that Lord of the Quadroads now owed Grog a favor!

When Pike learned about the deck, she was just as curious as Grog, but convinced Grog to wait until a very special occasion to pull the next one.

The Third Pull
After the defeat of Vecna, Grog in Whitestone decided to pull a card from the deck to celebrate the banishment of a lich-god. Pike arrived just in time to see Grog pull a card, but decided to just do nothing: preferring to watch and see what happened. Grog pulled "Void": his soul was immediately sucked from his body and contained in an object in a place of the DM's choice. One or more powerful beings guarded the place, and Grog's body was incapacitated while his soul was being held that way. A Wish spell couldn't restore Grog's soul, but it did reveal the location of the object holding his soul.

For the sake of the epilogue, the rest of the party (returning to their lives and relaxing) found Grog's catatonic body. Vex took the deck from Grog's body. Scanlan immediately proposed a toast: "To Grog! He was the dumbest of us all. He was the dumb and the dumb." To which Percy responded, "May he rest in bed sores for all eternity." Vox Machina then spent two weeks making their way through the halls of Pandemonium. Keyleth was furious because she thought she should be mourning, and instead she was hunting Grog's "stupid ass" down. Vex convinced her that it was keeping her occupied. Grog woke up in a chair in Whitestone Castle, surrounded by his VERY angry friends. Vex told him he was lucky that they didn't shave his beard for what he did. A horrified Grog realized that he fucked up. Scanlan successfully deceived Grog into thinking that Percy lost an arm in the process of rescuing his soul.

Trivia

 * It is unknown who previously owned the deck that Grog found in Thordak's lair.
 * Vox Machina's Deck of Many Things had 13 cards. As a result, the only way to undo Grog's curse would have been to ask a god for help. However, due to the manner in which Grog acquired the curse, no one knew to ask the gods the group bargained with for this aid.
 * Matt played cards as disappearing permanently from the Deck when drawn, though most cards reappear in the deck in the DMG version. This left Vox Machina's deck with 10 cards at the end of the campaign.
 * Grog pulled five cards from the Deck of Many Things during the Level 17 Battle Royale: Ruin, Rogue, Star, Key, and Knight.
 * According to Laura, Void is the worst card you can draw.