Blizzard’s beloved Diablo series of action role-playing games is about to celebrate its 20th anniversary, but the celebration looks like it will be sneaking into another Blizzard title in a pretty wacky way.

Fans have known that Blizzard is planning a Diablo 20th Anniversary Event in World of Warcraft for some time now. Taking place from Jan. 4-10, 2017, the event will allow players to earn special Diablo-themed items, including a twelve-string guitar toy and a super-large "Horadric Satchel" bag to expand their inventory space. But how will players earn these gifts?

YouTube video creator MabusGaming believes he’s cracked the code. In the video above, he runs down his theory for why he believes World of Warcraft is about to get a secret cow level.

For the uninitiated, the cow level is a joke dating back to the first Diablo, where fan rumors raged about a hidden area populated by deadly bovine opponents. That secret zone did not, in fact, exist in the first game. With Diablo 2, Blizzard added a method to create a special portal to the secret cow level, where players could face off against an army of cows armed with polearms. There was even an extra-difficult "Cow King" final boss.

So how does this relate back to World of Warcraft? The achievement WoW players can unlock for taking part in the Diablo 20th Anniversary Event includes the text "There is no cow level," a phrase Blizzard put into popularity with the release of Diablo 2. While digging into the just-released Patch 7.1, MabusGaming found a number of strange new spells: one named "Moo," one titled "The Secret Cow Level" and, naturally, one named "Summon Portal to Cow Level."

MabusGaming goes on to note that these spells could just be jokes on Blizzard’s part. They don’t guarantee the existence of a real secret cow level in World of Warcraft. But isn’t it more fun to believe?

We’ll likely hear more about Blizzard’s plans to celebrate Diablo’s 20th Anniversary next week at BlizzCon. Polygon will be reporting live from the event with any news about Diablo, as well as what’s next for World of Warcraft: Legion. That kicks off Friday, Nov. 4 at 11 a.m. PT.