Season 1 of Diablo 4 features the unique temporary mechanic of gathering Malignant Hearts from corrupted monsters and harnessing their power in the form of Caged Hearts, and the best way to farm Malignant Creatures to gather these Hearts is from the six Malignant Tunnels. These themed dungeons are special locations where corrupted beasts have sprung up after the events that Lilith caused in the main campaign. Malignant Tunnels serve as a part of the Seasonal questline but then become areas for players to return to farm the Malignant Creatures that are lying in wait within.
These six Malignant Tunnels in Diablo 4 are located throughout Sanctuary, with two in Fractured Peaks, two in Hawezar, and two in The Dry Steppes. The Tunnels are designed to be more user-friendly for players with less backtracking and more focus on killing monsters and getting rewards. Each of the tunnels has randomized layouts but will include the same general theme and enemies. Malignant Tunnels are marked on the map with the same icon as other Dungeons, but with a green leaf to differentiate them. Hovering over one on the map will indicate which type of Malignant Invoker a player will need to craft with Cormond or obtain before entering that Malignant Tunnel.
6 Den Of The Blighted
Diablo 4's Den of the Blighted is a Malignant Tunnel in the southern part of the Dismal Foothills in the Hawezar region and requires a Vicious Malignant Invoker. Unfortunately, this Tunnel simply doesn't have anything very impressive about it and its mob density is lower than other Tunnels, making it more of a time sink than anything. It is quick and easy to reach, however, as it's in close proximity to the Rakhat waypoint. Den of the Blighted has a larger variety of enemies, both normal and elites, which can help to mix things up some, but otherwise, it just doesn't seem as good for farming as the others.
5 Fissure Of Malice
Fissure of Malice is in the southwestern part of The Pallid Glade in Diablo 4's Fractured Peaks region, just south of Nostrava. This Malignant Tunnel requires a Devious Malignant Invoker and has a decent variety of enemies such as undead, Iron Clan, and more. In the objectives for the Tunnel, players will need to slay two Malignant Ghouls, Rakka and Shakka, which often are located pretty far away from each other and can require quite a bit of tedious exploration to find them depending on the randomization of its layout.
4 The Boiling Wound
The Boiling Wound Malignant Tunnel is located in the southeastern part of the Frigid Expanse in the Fractured Peaks, just east of Malnok, which makes it pretty quick to reach from several of the waypoints in the area. Players will need a Devious Malignant Invoker for this Tunnel, but it is a great one when someone is short on time. The Boiling Wound is the shortest Malignant dungeon in Diablo 4 Season 1, which is helpful for players who want to rush to the Malignant Outgrowth at the end quickly to get a specific Malignant Heart.
3 Dindai Hollow
Dindai Hollow is a great Malignant Tunnel for farming lots of XP and Malignant Hearts in Diablo 4. It is located in the Dry Steppes region, in the western part of Dindai Flats, but sadly it is not within very easy reach of any waypoint. This dungeon features a heavier focus on Elite Enemies at the beginning of the Malignant Tunnel, which is helpful for farming, and has a fairly short layout overall that makes it easy to run multiple times while a player is in the area.
2 Bedeviled Grotto
Besides having the best name of the Malignant Tunnels, the Bedeviled Grotto generally features the most ideal layouts and heavy mob densities which provide high amounts of XP. This dungeon is located in the Blackguard Bog of Hawezar near Backwater's waypoint and needs a Vicious Malignant Invoker. The enemies in the Bedeviled Grotto are mostly Serpent Cult members and Nangari creatures, including a Malignant Elite Nangari named Alcanthe. This is one of the longest Malignant Tunnels in the game, but offers a lot of rewards in XP and Malignant Hearts to make it a worthwhile endeavor.
1 Ravening Pit
Diablo 4 Season 1's Ravening Pit is the best Malignant Tunnel to farm Malignant Hearts, including the most powerful variety, Wrathful Malignant Hearts. This Tunnel in the eastern portion of Untamed Scarps in Dry Steppes requires a Brutal Invoker and has a Dungeon objective "Slay 2 Elites," which gives even better odds for farming as the Elite enemies are a good way to get additional Malignant Hearts.
One tip if a player is looking specifically for Wrathful Hearts is to enter this Malignant Tunnel and run around to find the Elites, and if they are not Wrathful Elites the player can leave and reset the Tunnel and try again. The layout of this Tunnel makes it generally pretty easy to do this, as long as one is careful not to get too many strong enemies chasing them at once.
Each of these Malignant Tunnels has small objectives that must be completed before moving through different sections, and all are great places to farm for Malignant Hearts, so it can be fun to mix things up some and not simply do the same one on repeat throughout Season 1. Even if the Malignant Hearts that drop are not what a player is looking for, they are worthwhile for crafting Malignant Ichor with Cormond, which are needed for crafting Malignant Invokers. Diablo 4's Malignant Tunnels are a limited-time event for Season 1 only, after which time there will be an all-new focus with Season 2.
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