The hills have arms (and they're beating your ass)

Elementals

Certain ideas are on their face kind of lame or frustratingly executed, but have a kernel of something resonant that keeps bringing you back. It's like the flaws are there to taunt you, challenging you to fix them. 

Old school D&D is like that. BX is a terrific game with enough tremendous flops and oversights that designing house rules and derivative systems has essentially become a hobby in and of itself.

D&D elementals also fall in this category. People have been providing new rules, alternative interpretations, and added texture for decades. Chris Hogan has a good writeup on why elementals are boring and what can be done about them, and it's from way back in the day when people started their posts with a Captain Planet reference (it's good though and you should read it. No one posts like that anymore). 

A lot of people go in the direction of adding layers nuance to elementals and changing the baseline assumptions. This post from Scrap Princess has been knocking around my brain for years, and even though I haven't found a use for it in my game it's a welcome addition to my mental ecosystem. "Gravity fire" is a good example of the kind of radical direction people take the elemental concept.

I like this approach a lot, but when you change elementals too much it requires a lot more buy-in from the players. The baseline concept for elementals is so easy to grasp it almost feels too straightforward, but hear me out: A wildfire is scary, but a sentient wildfire that's trying to kill you, specifically, is terrifying, exhilarating, and somewhat absurd—perfect for a D&D game. Living tornados and walking earthquakes might not be the most glamorous (certainly underserved by the official art) but damn it they can be fun too. They're like those OSR-style challenges we all go crazy for but with hit points. 

The problem is, nothing about this is reflected in the stats. We're led to believe elementals are living  flames/winds/water/earth but you can walk right up to one and whack it with a sword? And the only risk you run is being targeted by its one attack per round? Something's not right here.

This is just a side-note before I move on, but a point I've never seen mentioned before is the monster listing for elementals in both O and AD&D imply they are only the stats for conjured elementals (either by staff, spell, or device). The AD&D Monster Manual even goes so far as to specify more sophisticated elementals exist "than can be summoned." Over time, these "conjured elementals" became the standard all-purpose elemental, leading to the uncomfortable middle ground we have today where they're kind of mindless bag-of-hitpoint monsters but are also supposed to be the dominant lifeform on their respective plane, which supposedly all have their own cultures and civilizations.   

What D&D does well

Conjured elementals map neatly to things high-level characters will do, namely aerial adventures, seafaring adventures, domain-level stronghold sieges, and messing around with large quantities of fire.

When a magic-user conjures an elemental it requires their full concentration to maintain control. This implies elementals are like bound spirits held against their will, which is very on-theme. Elementals summoned by druids don't turn on their masters, probably because they asked nicely. 

Little details about how elementals’ size changes based on their power and how fire and earth elementals are obstructed by channels of water are nice and lend some tactical depth for keen parties to leverage. 

Treating elementals as extraplanar entities instead of constructs gives elementals an appropriately numinous quality, even if their statblocks don’t measure up. 

In AD&D, certain spells require the presence of an elemental or become stronger if an elemental is used in their casting. This is only true for earth and air elementals (distance distortion and move earth for earth, call lightning for air) but there’s a lot of potential for this to be expanded. Magic-users conjuring planar beings to aid their spellcasting is exceptionally evocative and I’ll most definitely steal that idea. 

This is how elementals work now

Elementals are formed when essence from the planetary lifestream is sequestered in base matter—in the D&D world, this means fire, water, earth, and air, instead of like atoms or whatever. 

Digression: There's no elemental plane of air/fire etc. There is only one elemental plane, and it surrounds and touches this one at all points. The elemental plane—wizards call it the Plane of Elemental Anima, capitalized—is where the world's living essence exists in tangible form. It's also the place where beings like animistic nature spirits, djinns, and all those weird elemental monsters from the Rules Cyclopedia like helions and the kryst reside. Barbarians call the elemental plane the "Godrealm," as that is where their many heathen deities originate. 

Conjured elementals, generally, should not be dealt with as typical monsters. Mundane weapons are useless, and magical weapons only deal minimal damage unless specifically designed to harm enchanted or extraplanar creatures. Damage to an elemental's corporeal form is just reconstituted from the surrounding element.

The most common way to defeat an elemental is by depriving it of its matter. Cut off a water elemental from its source, trap a wind elemental in a vacuum, uproot an earth elemental, deny a fire elemental access to fuel. 

Smart players would go after the commanding MU to break their concentration. You'd think most MUs have contingencies in place to prevent this from happening, but evil wizards have a habit of underestimating plucky adventurers.

The easiest way to handle an elemental is by commanding another to fight it or casting a spell of banishment. The problem is, this requires collaboration with powerful MUs and/or clerics, who are rare, expensive, and hard to get along with in equal measure. 

Elementals also have utility, believe it or not, outside of combat. Their life essence can be channeled to manipulate their native element. [design note: RAW conjured elementals exist indefinitely until slain or dismissed. I like the idea of using elementals for non-combat activities but if they last forever they would be too useful and unbalance the game. Exchanging hp for more capabilities is my compromise.]

Here are the stats to make conjured elementals more like the primordial forces of nature they ought to be: 

Air

Appearance ideas

8 HD:  Airborne debris flying like a starling murmuration

12 HD: A screaming, whirling disk of silvery cloud-stuff. Whizzes around recklessly.  

16 HD: A storm cloud serpent with thunderbolt wings 

AC 2/0/-2 Att. +7/+9/+11 blow (1d8/2d8/3d8) Mv. 360'(120') flying Saves: as HD Morale: 10 Alignment: Neutral

• Must be conjured under the open sky.
• Deals an extra 1d8 damage to flying foes. 
• Creatures less than 2 HD in melee range must save vs. death each round or die from suffocation.
• In place of doing damage, hit creatures up to ogre size can be flung 1d4x10' in any direction, taking fall damage as applicable. 
• Dissipates if trapped indoors or in other enclosed spaces.

Additional powers

• Thunderclap. Costs 2d8 hp. Releases a concussive burst that can be heard for miles; creatures within 50’ must save vs. breath or take 2d12 damage and be deafened and stunned (half movement and -4 to attack rolls) for 2d6 rounds, half damage on a success.
• Tailwind. Costs 2d8 hp per hour. Allows sailboats and aerial vessels to move at 1.5x speed.

Earth 

Appearance ideas

8 HD: Upper body like a man, lower body like a giant earthen slug 

12 HD: A slouched ape figure with arms thick as tree trunks 

16 HD: A seismic wave-hill that drags itself on four giant pillar-like appendages 

AC 2/0/-2 Att. +7/+9/+11 blow (1d8/2d8/3d8) Mv. 60'(20') moves freely through unworked earth Saves: as HD Morale: 10 Alignment: Neutral

• Must be conjured from raw dirt, stone, sand, or clay.
• Deals an extra 1d8 damage to structures and foes on the ground.
• In place of attacking, can create a tremor that causes everyone in 20' to fall over and save vs. paralysis or take 1d6 damage. 
• Cannot cross a water barrier wider than their HD in feet.
• Dissipates if uprooted from the earth. Explosives harm earth elementals, as does falling, which kills them outright. Large scale excavation equipment deals normal damage—a human with a shovel won't do anything, but a giant with a giant shovel is a different story.

Additional powers

• Liquefaction. Costs 2d8 hp. The ground in a 30’ radius becomes quicksand.
• Land formation. Costs 3d8. The elemental forms itself into a shape of whoever commands its choosing (wall, pillar, small hut, etc.). Total volume of earth available to manipulate is 400/600/800 cubic feet. The elemental is inert while shaped (yet still conscious), and must lose another 3d8 hp to return to its original form. MUs still need to maintain concentration while an elemental is shaped, or else it will slip from their control and revert to its original form. 

Fire

Jon Silent

AC 2/0/-2 Att. +7/+9/+11 blow (1d8/2d8/3d8) Mv. 120'(40') Saves: as HD Morale: 10 Alignment: Neutral

Appearance ideas

8 HD: Hundreds of small flaming figures dancing and leaping, their heads like tiny stars.

12 HD: A riotous vortex of fire unfurling like a rose.

16 HD: A plasma toroid hovering ominously above the ground.

• Must be conjured from a roaring fire of at least man-height.
• Automatically damages foes in melee range. Ignites flammable material.
• Cannot cross a water barrier wider than their HD in feet.
• Loses 2 hp each round it lacks access to fuel (dry firewood, oil, etc.).

Additional powers

• Combust. Costs 2d8 hp. Deals an amount of damage equal to hp lost to every creature within 30’, save vs. spells for half. Any amount of additional hp may be spent to bolster the effect.
• Primordial crucible. A fire elemental can be bound in order to reduce the time (but not the cost) of creating a magic item by 1 week per HD. There's a 10% chance each week the elemental escapes from it's binding and attacks it master, ruining the magic item in the process. The elemental dissipates once the magic item is created, and can be dismissed at any time—for example, an MU can decide that after shaving 8 weeks off a 6-month project they don't want to risk it any more, they can dismiss their elemental and work the remaining 4 months alone. 

Water

Appearance ideas

8 HD: Wriggling mass of transparent worms

12 HD: A broad ribbon of water, gently swaying

16 HD: A roiling black water leviathan with glassy sheen, flecked by sparks of bioluminescence

AC 2/0/-2 Att. +7/+9/+11 blow (1d8/2d8/3d8) Mv.  60’(20’) on land, instantaneously disperses and reconstitutes anywhere in a 180’ radius while in water. Saves: as HD Morale: 10 Alignment: Neutral

• Must be conjured from a body of water no smaller than a pond or creek.
• Deals an extra 1d8 damage to foes in water.
• A water elemental can attempt to surround and submerge a foe by moving into the space it occupies. Save vs. paralysis or be restrained by the elemental and unable to breathe (losing consciousness in 2 rounds). On a successful save the creature is pushed back 10’. 
• Dissipates if more than 60’ from its water source.

Additional powers

• Phase change. Costs 1d8 hp. Elemental becomes mist, ice, or turns back to water. It can freeze around submerged foes, trapping them and inflicting 1d6 damage as they get crushed by expanding ice.
• Maelstrom. Costs 1d8 hp per round. Elemental creates a giant whirlpool that sucks boats and traps aquatic creatures. Potentially surfaces submerged treasure or awakens abyssopelagic sea monsters.