Sludgefist is a single phase "patchwerk" style encounter in which the raid needs to defeat this hulking monstrosity before he removes all four pillars in the room and then slams into a wall with his Hateful Gaze. This fight requires on the fly coordination, as the boss will tether random players together with Chain Link that will likely kill the players if broken. The fight takes place in the same space as the Shriekwing encounter.

Sludgefist is the first boss in the final Upper Spire wing. 

Sludgefist Quick Tips in Castle Nathria

• Stay within 15 yards of your partner at all times when afflicted with Chain Link.

• Both tanks should stand on each other at all times to share the damage from Giant Fists.

• When marked by Hateful Gaze, hide behind a pillar to make the boss run into it. Everyone else should avoid standing in this path!

• Align DPS cooldowns to take advantage of the Destructive Impact damage increase the boss has whilst stunned after hitting a pillar.

• Position the boss 20+ yards away from pillars at all times to avoid breaking them with Destructive Stomp.

• Run 20+ yards away from the boss when he casts Destructive Stomp.

• Ranged players should stay far from the boss to bait Falling Rubble into low traffic areas.

• Colossal Roar deals damage and pushes you back... avoid getting pushed back into Stonequake zones!

• The boss gains a Gruesome Rage at low health... finish him off quickly!

A full guide can be found on Wowhead: https://www.wowhead.com/guides/sludgefist-castle-nathria-raid-strategy-guide