Elemental Form: The Guardian has one of 4 Elemental Forms: Earth, Fire, Air, Water

Immunity to damage type of Elemental form

Multiattack: The guardian makes two melee attacks and can use Elemental Manipulation.

Melee Attack: +10 +10 to hit, reach 10 ft., one target. Hit: 23 (3d8 + 10) (3d8 + 10) bludgeoning damage +5 (1d8) (1d8) of current element Type .

Elemental Blast: (Recharge 5–6)The guardian releases a blast of elemental energy in a 20-foot cone. Each creature in the cone must make a DC 18 Dex saving throw. On a failed save, the creature takes 35 (8d8)(8d8) fire, cold, lightning, or thunder damage. 1/2 on success

Elemental Manipulation: The guardian can control one of the four elements: fire, cold, lightning, or thunder. It can use this ability to create elemental effects, such as summoning elemental creatures, controlling the weather, or altering the terrain.

Fire: Temperature of room increases (Each Character takes 1d4 fire damage at start of thier turn +1d4 per usage)

Earth: All terrain becomes difficult subsequent usage ranged attack (+10 to hit) against one target:,1d10 bludgeoning damage as rocks are tossed in the air

Air: All movement that touches the air (i.e. not burrowed) is halved. Missile attacks have disadvantage. Subsequent usage ranged attack (+10 to hit) against one target 1d8 lightning damage as the air becomes statically charged

Water: Temperature of room decreases (Each Character takes1d4 cold damage at start of their turn +1d4 per usage)

Elemental Shift: The guardian changes its elemental type to one of the other three elements (fire, cold, lightning, or thunder). This affects its elemental blast and elemental manipulation abilities.

It gains the following:

The Elemental Guardian gains 20 Temp HP

• Earth Form:
  • Earth Glide: The Guardian gains a Burrow Speed of 30 and can burrow through nonmagical, unworked earth and stone. While doing so, the elemental doesn't disturb the material it moves through.
  • Successful melee attacks can push the target 10ft (DC 18 Strength save)
  • Element Type: Thunder
• Fire Form:
  • Fire Wake: Speed Increases to 50
  • Fire Body: A creature that touches the elemental or hits it with a melee attack while within 5 feet of it takes 5 (1d10) fire damage. In addition, the elemental can enter a hostile creature's space and stop there. The first time it enters a creature's space on a turn, that creature takes 5 (1d10) fire damage and catches fire; until someone takes an action to douse the fire, the creature takes 5 (1d10) fire damage at the start of each of its turns.
  • Element Type: Fire
• Air Form:
  • Gains a Fly speed of 90 (hover)
  • Lightning Launcher: Its melee attack gets a range of 30 ft and does all lightning damage. 
  • Element Type: Lightning
• Water Form:
  • Gains a swim speed of 90ft. 
  • Freezing Depths: creatures with in 5ft of the Guardian take 5 points of cold damage at the start of their turn.
  • Element Type: Cold

The Elemental Guardian can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The Elemental Guardian regains spent legendary actions at the start of its turn. Recharges are rolled at the start of the Elemental Guardian's turn. 

Slam Attack: The guardian makes a melee attack.
Elemental Dash: The guardian moves up to 30 feet without provoking opportunity attacks, its form shimmering and shifting between the elements as it does so.
Elemental Tempest: (Recharge 5–6)The guardian expends two legendary actions to unleash a devastating elemental burst. It deals 50 (10d10)(10d10) damage of its current elemental type in a 30-foot radius. Creatures within the area must make a DC 18 Constitution saving throw and take half damage on a success.

Elemental Flux: The guardian can use Elemental Shift. 

Legendary Resistance: If the guardian fails a saving throw, it can choose to succeed instead. It can only use this feature once per form (does not regenerate when using elemental shift, i.e. uses LR in earth form switches to fire can use LR, switch back to earth, no LR) per day.