Argoros, Remnant Core (RAID BOSS)

Raid Boss. The golem as a number of associated mechanics that are integral to its fight. See the Mechanics section for more detail

Mechanicous Necessitous. The golem always goes first in the initiative order

Partial Shielding. Each time the golem appears at a table, it reapplies its Partial Shielding, causing it to be resistant to all damage except thunder (which deals normal damage) until hit with an Elemental Bolt 

Segmented Fight: The golem has 6 separate health bars with 60 health each. Each time a health bar is depleted, it leaves the current table it is at, recharges its Core Charge, and appears at the opposite table on its turn. After the 3rd health bar is depleted, it becomes Enraged and gains access to features marked with Enraged.

Desync Protection: If the golem is ever at a table for more than 3 rounds consecutively, it leaves and goes to the other table.

Raidboss Resistance. The Golem is immune to any effect that would change its shape, teleport, knock it prone, or send it to another plane.

Magic Resistance. The golem has advantage on saving throws against spells and other magical effects.

Magic Weapons. The golem's weapon attacks are magical.

Elemental Fracture: When the golem appears at a table, it designates 3 Segments to be targeted with Elemental Fractures. At initiative count 0, the three Segments will be destroyed and can be rebuilt with a successful Repair Protocol. Creatures standing on a Segment when it is destroyed take 10 (3d6) force damage and are knocked back to the nearest unoccupied space.

Enraged Resistor: While the golem is enraged at the start of each of its turns it may choose a Segment to electrify until the start of its next turn. While electrified, the space is difficult terrain and creatures that end their turn on the square take 5 (1d6 +) lightning damage.

Final Stand: When the golem's last health bar is reduced to 0, it moved to the center of the chasm and turns one hand toward each table, charging a massive attack. Players must deal 100 total damage (50 each side) to defeat the boss. While this attack is charging, the golem cannot take actions or legendary actions.

Multiattack. The golem makes any combination of 2 melee or beam attacks

Enraged Mulitattack. The golem makes any combination of 3 melee or beam attacks

Slam. Melee Weapon Attack: +7 to hit, reach 15 ft., one target. Hit: 11 (2d6 + 4) bludgeoning damage.

Beam. Ranged Weapon Attack: +7 to hit, range 120 ft., one target. hit: 9 (1d8 +4) fire damage.

Core Charge (Recharge 5-6). The golem creates a 5x120 foot long line emanating from itself. All creatures in the line must succeed on a DC 14 dexterity saving throw or take 13 (4d6) fire damage and be knocked prone

The golem 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 golem regains spent legendary actions at the start of its turn.

Slam(Costs 1 action): The Golem makes a slam attack

Beam (Costs 1 action): The Golem makes a beam attack

Move(Costs 1 action): The Golem moves up to its movement speed

Missile barrage (Costs 2 actions): The Golem targets up to 6 creatures it can see within 300 feet of itself. Each creature must make a DC 14 dexterity saving throw or take 9 (1d8 +4) fire damage and be knocked prone. Creatures who succeed on this save take half damage and are not knocked prone. 

Mechanics:

Argoros has a number of mechanics that are to be presented in addition to its stat block. The mechanics are as follows:

Segments: The arena is a 11x11 square (using a 5ft grid) with an additional 3x3 space directly south (housing the Elemental Ballista). The arena is walled on the east, south, and west sides, but open to a bottomless pit on the north side.

There is a 5 foot wide catwalk that rounds the edges of the arena. The rest of the arena is divided into 9 total 3x3 squares arranged in a 3x3 grid with a 5 foot wide catwalk around the edges of the arena. Each 3x3 square is called a segment and can be destroyed by the Elemental Fracture feature.

A segment can be repaired by a successful Repair Protocol. Creatures standing on a Segment when it is destroyed take 10 (3d6) force damage and are knocked back to the nearest unoccupied space.

Repair Protocol: When the boss is not at the table, a number of Repair Nodes equal to twice the number of broken Segments will appear, each color coded into pairs and on opposite sides of the field from each other.

Each Repair Node pair will have one Origin and one Receiver. Players can activate a Repair Node Origin as a free action while within 5 feet of it, or with any source of damage. Once a Repair Node Origin is activated, a beam of energy will emerge from it and connect to the nearest allied creature within 10 feet. From there, the beam will jump from creature to creature within 10 feet of the last connection until it reaches the Repair Node Receiver. Once a link has been established between the Repair Node Origin and Receiver, one Segment of the players choice will reform. 

Elemental Ballista: When the boss leaves the table, 4 Elemental Motes will spawn. an Elemental Mote is a tiny elemental with 11 hp, an AC of 12, and each have the Beam action from the Argoros' stat block. Elemental Motes drop Elemental Charges when killed. 
Elemental Charges can be picked up by a player (or their bonded) by occupying their space and can be thrown up to 60 feet as a bonus action. When a player picks up an elemental charge, they regain 5 hit points.

When an Elemental Charge is thrown at the Elemental Ballista, the ballista gains 1 Charge. When the ballista is at 3 Charges it can be commanded as an action by a creature within 5 feet to fire an Elemental Charge at Argoros to break its Partial Shielding. Firing the Elemental Ballisa removes all charges from it. For each Charge above 3 the Elemental Ballista is holding, it deals an additional 10 (3d6) force damage to Argoros when it is fired.

Additional Spawns: Whenever Argoros is not at a table and there are no Elemental Motes on the field, 2 Elemental Motes spawn in unoccupied spaces on the battlefield.

Lethality Protection: At any point during the fight if the players are running low on resources or health, you may add the following mechanic: Firing the Elemental Ballista restores 5 health to all allied creatures on the battlefield (at both tables)