By Alan McCoy from Dungeons & Dragons: Fundamentals
How to build challenging encounters against an Earth Elemental
Note: This has been prepared utilizing only the 5E Core Rules. The Earth Elemental can be found in the Monster Manual page 124.
Earth Elementals are summoned, not evolved creatures, as such they have no specific form, they can be bound into a shape by the will of their summoner/creator. When speaking of Earth Elementals, these terms can be used interchangeably. When summoned without a specific shape requirement, they tend to take a shape that fits their nature. Earth Elementals tend to appear as a large four limbed rocks with a vague shape of a face.
An Earth Elementals cannot be summoned in an area unless there is a significant volume of earth or stone present.
Step 1) Let’s review what we know about the Earth Elementals.
Earth Elementals are extremely strong and tough, they have very little personality or intelligence. They move slowly for a creature of large size, walking a mere 30 feet each round. They can burrow just as fast however, and with their earth glide ability, they leave no trace of their passage.
Earth Elementals take half damage from non-magical bludgeoning, piercing and slashing attacks, and are immune to poison attacks.
Earth Elementals are unaffected by Exhaustion, Paralyzation, Petrification, Poison, or unconscious conditions. They do not need to consume (eat or drink), breathe or sleep.
Earth Elemental Senses include: Darkvision 60 foot, Tremorsense 60 foot, and a passive Perception of 10.
Earth elementals are vulnerable to Thunder Damage.
Earth Elementals are living siege engines, doing double damage to objects and structures.
Step 2) Determine the probable Strategy
Earth Elementals are constructs that exist only to serve their creator. They do come with certain default combat techniques built in that serve much like the instincts of an animal. They are not adaptable however and will continue even a losing strategy unless directed by their creator. These elementals maintain a telepathic link to their creator if that creator remains within 120 feet. The creator can receive the sensory input of the elemental.
Step 3) Determine Tactics
The primary attack is of course their multi-attack slam, using their powerful fists to bash their target into submission. This attack has a 10-foot reach. This attack is often used to bash apart structures or other inanimate objects as directed by the creator.
These creatures are aware of their vulnerability to Thunder damage, and anyone who makes an attack within range of their tremorsense will become their primary target unless their creator orders otherwise.
These powerful creatures that would seem to be no more than brutes, but they do have a few programed techniques available to them.
Technique #1: Earth Glide – The Elemental may move through unworked natural rock, earth and stone as if it were liquid. They can step into it to disengage, move to the position desired and resume attacking. While burrowing, the elemental is immune to most attacks.
Technique #2: The Shove – The Elemental can sacrifice one of its slam attacks to shove an opponent back five feet. It will do this if the target is near the edge of a drop-off or otherwise could be endangered.
Technique #3: The Grapple – The Elemental can wrap its arms around a target and carry it into an inhospitable environment, such as underground.