By Alan McCoy from Dungeons & Dragons: Fundamentals
How to build challenging encounters against a Umber Hulk
Note: This has been prepared utilizing only the 5E Core Rules. The Umber Hulk can be found in the Monster Manual page 292.
Umber Hulks are creatures of the deep earth, and will only be encountered in the Underdark, deep cave complex or perhaps a deep level of a dungeon. It is difficult to keep an Umber Hulk someplace it doesn’t want to be. The tunneller feature turns even solid rock into mere difficult terrain.
Step 1) Let’s review what we know about the Umber Hulk
Amazingly Strong and very tough, above average dexterity, its mental abilities are on par with human normal, this is extraordinarily high for a monstrosity.
Umber Hulks are Large creatures standing eight feet tall or better, they have steel hard chitin for a body, usually scarred from the cave-ins that the creature has survived. They possess large mandibles and have two huge claws that can tunnel through solid stone. They have four eyes, two large ones and two small ones. The eyes are a bewildering myriad of colors and motion.
Senses: Darkvision 120 feet., Tremorsense 60 feet. Passive perception 10
Movement: 30 feet, Burrow 20 feet.
Tremorsense is the ability to utilize motion to determine your surroundings. The Umber Hulk does this with its hair-like feelers.
Step 2) Determine the probable Strategy
Strategy is dependent on what the creature wants, and what it is willing to do to get it. These monsters are not, despite their appearance, mindless brutes. The Umber Hulk is a thinking creature that has a language and that can plan and react. Instinct doesn’t control them.
What is known is that the Umber Hulk has been known to feed on a variety of organic material. Purple Worm, Ankhegs, or Men, basically anything Soft and fleshy.
Step 3) Determine Tactics
Umber Hulks are Ambush Attackers that will stand in wait of a prey animal to come near, Usually on the other side of a foot or more of solid rock. Note that ‘the other side’ can mean above, below or to the side of the passage being traveled by the party.
Additionally, as Umber Hulks are intelligent and can SEE with their tremorsense the way we see with our eyes, they can also detect the unarmored and more vulnerable targets in a group.Remember that an Umber Hulk can burrow even through solid rock at the rate of 10 feet every six seconds. Mere packed earth or loose stone at 20 feet every six seconds.
Because it is waiting on the other side of a solid physical barrier, it is highly likely that the Umber Hulk will be entitled to a first strike from hiding (Advantage).
It is possible that the Umber Hulk will be entitled to a surprise round, that will have to be determined by the individual DM.When attacking the first thing you should check for is light sources. If any exist. the Confusing Gaze Feature of the Umber Hulk comes into play. This is not an action on the part of the Umber Hulk, merely the side effect of being able to see its eyes. (DC 15 Charisma Saving Throw).
Because they are thinking creatures and aware of effect their gaze can cause, they will utilize luminous material such as rock fungi or a fire beetle’s glow to specifically to illuminate its eyes and allow its confusion ability to come into play.
As an intelligent creature aware of the confusion its eye gaze causes, the Umber Hulk will make a quick scan of the group to determine if any are confused (DC 10 Perception check may be resisted by insight), if it detects any it will attempt to target grapple that person and drag them off to its lair. (MM page 11 – the DC for escaping an Umber Hulks Grapple would be 10 + Str Mod = 15; Rolled with disadvantage unless the target was also size Large.
Umber Hulk prefer smaller targets, namely Gnomes and Halflings, because their movement is halved when carrying a size Medium target.
Unfortunately for the Umber Hulk, they leave a tunnel in their wake, and they can be easily followed. Unless in solid rock, the Umber Hulk can spend an action collapsing the tunnel behind them.
If it chooses to fight, the Umber Hulk has a powerful multi-attack combination involving both claws and one with its mandibles.
Whenever possible, it will face its opponents and DODGE for a few rounds to allow it’s confusing gaze to effect as many as possible, then attack with its claws and mandibles.If forced to retreat, it will Dodge for a few rounds, to allow the confusing gaze to disorient, dodge for a round or two, then disengage, and/or dash away (with its latest meal if possible).