The 20th anniversary Darkening of Tristram event in Diablo 3: Reaper of Souls is now live, and here’s how to unlock the Butcher pet in the new 16-level retro dungeon.

Even though the game is nearly five years old at this point, Blizzard has continued to support Diablo III with regular updates. The latest update for the game, 2.4.3, adds the limited-time 20th anniversary event called The Darkening of Tristram. The draw of this event is the chance to play through a dungeon with retro graphics, sound effects, and gameplay, complete with items and monsters from the original Diablo game. Additionally, the Butcher, a cleaver-wielding boss from the original Diablo, can be claimed as a pet in Diablo III as a part of the event.

After downloading the 20th anniversary update for Diablo III, players will have the chance to complete a 16-level dungeon while playing in Adventure Mode (itself unlocked by completing the game at least once). Most players will be tempted to go through the new dungeon with their favorite character, but to get the Butcher pet, players need to go in with a completely fresh character.

This could have been problematic, but luckily, any difficulty level will suffice, and the dungeon itself is not terribly difficult. Any experienced Diablo player should have no problem hacking and slashing their way through the dungeon, but there are a couple more things to keep in mind before trying to unlock the Butcher pet.

Diablo 3 Adds Diablo 1-Style Dungeon and Bosses - Diablo box art

First off, players will need the Reaper of Souls expansion downloaded for Diablo III on PC, PS4, or Xbox One (Xbox 360 and PS3 owners are left out of the event). Secondly, players have to complete this dungeon without turning off their game. However, if players decide to leave in the middle of the dungeon and return to town for supplies or to drop off loot, then they shouldn’t have to start the process over from the beginning. Not being able to turn off the game may be frustrating for some, but it’s worth noting that the dungeon should take less than an hour for most players, so starting over isn’t the end of the world.

Something else to keep in mind is that players can’t gain any XP outside of the new dungeon. For one reason or another, players are expected to go straight to the limited-time event dungeon and only start killing monsters while inside, otherwise they will miss out on unlocking the Butcher pet and will have to start the process over with a new character.

With these things in mind, basically all players have to do is complete the new dungeon. As long as they do it without dying, with a new level 1 character, and without turning off their game for any reason, they should unlock the Butcher pet as a reward for fighting their way through all 16 levels of the retro dungeon.

Anyone that misses out on the Darkening of Tristram event and unlocking the Butcher pet should know that the event will return in the future. In fact, Blizzard has said that the 20th anniversary event will come to Diablo III every January, though it may one day be transferred to a fourth Diablo game instead.

Diablo III is available now for PC, PS3, PS4, Xbox 360, and Xbox One.