Shellder / Cloyster

Shellder is a bivalve mollusk Pokémon encased within a spiky, blue-violet bivalve shell. It has two round white eyes with tiny black pupils. Its enormously long red tongue is used to burrow itself into the sand to sleep overnight and also to lure and capture prey. The tongue protrudes even when its shell is closed and tugging it will cause the shell to pop open. Its soft and tender body is well-protected by its extremely durable shell, which is purported to be harder than diamonds and has historically been used by people to make shields. It can make pearls from accumulated sand, though it discards them as they are typically in its way.
Shellder has an unusually strong appetite for the tail of a Slowpoke and can develop a symbiotic relationship with the Dopey Pokémon. After attaching itself to the Slowpoke's tail, the two undergo a metamorphosis and evolve into Slowbro together. Alternatively, if it attaches to the head of a Slowpoke in possession of a King's Rock, the two will instead evolve into Slowking. These relationships allow it to travel onto land and begin a new stage in its life cycle. In Forian , Shellder attaches to the forearms and heads of Forian Slowpoke wearing Forian Cuffs or Forian Wreaths, causing the evolution into Forian Slowbro and Forian Slowking, respectively.
Regardless of which form the two evolve into, Shellder's shell transforms into a spiny, spiralled cone with several tiers. Sharp teeth develop around the rim of the shell to anchor it securely to the evolved Slowpoke, and its eyes now peek out from the bottom rim of the shell. In its crown form, Shellder will have a red jewel on its underside and a large horn on either side of its shell.
While in its crown form, Shellder will periodically release its venom into Slowking's brain. This is actually beneficial to Slowking, as it causes the Regal Slowking's intelligence to increase. Higher quantities of venom intensify this effect, and Shellder is easily provoked into releasing more whenever Slowking yawns. However, Shellder's poison makes Slowbro more sluggish as it continues to drain nutrients from its host's body.

Shellder

It swims facing backward by opening and closing its two-piece shell. It is surprisingly fast.

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Armor Class	15 (natural armor)
Hit Points	8d6+16
Speed	5 ft.	Swim 30 ft.
Strength	10 (+0)
Dexterity	10 (+0)
Constitution	14 (+2)
Intelligence	12 (+1)
Wisdom	10 (+0)
Charisma	10 (+0)
Damage Vulnerabilities	Lightning
Damage Resistances	Cold
Languages	Aquan
Challenge	1/4 (50 XP)
Special 1	Hard Shell	After Shellder uses Withdrawal,	it gains resistance to all damage until it takes another action
Special 2	Hold Breath	While out of water, the Shellder can hold its breath for 15 minutes
Special 3	Water Breathing	The Shellder can breath only underwater
Action 1	Clamp	Melee Weapon Attack	d20+2 to hit
Reach 5 ft., one target	Hit 1d6 bludgeoning damage	and the target is grappled (escape DC 10).	Shellder can only have one creature grappled at a time
Action 2	Withdraw	The Shellder withdraws its body into its hard shell and closes it tight.	Until it emerges, it gains a +2 bonus to AC,
and it has advantage on Strength and Constitution saving throws.	While in its shell, it is prone,	its speed is 0 and can’t be increased,	it has disadvantage on Dexterity saving throws,
it can’t take reactions, and only the only action it can take	is a bonus action to emerge from its shell

Cloyster is a black bivalve mollusk Pokémon. It is encased inside a light-gray shell, which is surrounded by a second jagged, blue-violet outer shell casing. It has one barb-like spike protruding from above its head, and multiple conical horns on its outer shell. Its shell is harder than a diamond with spikes that are even harder; harsh tidal currents will affect the size and sharpness of these spikes. On its pearl-like face, it has two white eyes and a mouth. Aside from its face and head, its internal anatomy has never been seen. Once it has shut itself in, it is impossible to open its shell from the outside. This impressive defense allows it to withstand anything from a bomb blast to even a missile strike.
Cloyster typically only opens its shell to attack an opponent. However, it is fully capable of retaliating against any enemy with its shell tightly closed. With rapid succession, it launches its spikes at the foe, keeping them repelled.
Variant: Adamantine Shell Armor
A Cloyster's shell is incredibly resilient and posses similar properties to adamantine. If you'd like to reflect that in the stat block, you have the option of improving its Shell Armor ability to where any critical hit landed against it becomes a normal hit. This has no effect on the Cloyster's challenge rating.
Using a Cloyster Shell
A Cloyster's shell weights about 300 pounds. An intact shell can sell for 3,000 GP.
Arctic tribes and hungers have long used shards from a CLoyster's sell for spears, daggers, and other piercing weapons, and recovered shards can be immediately wielded as the appropriate weapon. Form a whole shell, a skilled artisan can refine at least four pikes or spears, or twelve daggers. These weapons are unusually effective when used to attack objects. Whenever a Cloyster shell weapon hits an object, the hit is a critical hit. A Cloyster shell weapon has a value of 250 GP more than the normal version.
Alternatively, an entire Cloyster shell can be used to make a set of armor with the following properties:
Cloyster Shell Plate Armor
Armor (plate), uncommon This suite of armor is made from the resilient shell 0of a Cloyster. While you're earing it, any critical hit against you becomes a normal hit. Additionally, any creature that starts its turn grappling you takes 1d6 piercing damage.

Cloyster

Its shell is extremely hard. It cannot be shattered, even with a bomb. The shell opens only when it is attacking.

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Armor Class	19 (natural armor)
Hit Points	18d8+54
Speed	5 ft.	Swim 30 ft.
Strength	16 (+3)
Dexterity	10 (+0)
Constitution	16 (+3)
Intelligence	6 (-2)
Wisdom	10 (+0)
Charisma	10 (+0)
Saving Throws	Strength d20+6	Constitution d20+5
Skills	Perception d20+3
Damage Resistances	Cold	Piercing	Slashing from nonmagical attacks
Damage Vulnerabilities	Lightning
Damage Immunities	Cold
Senses	Dakrvision 60 ft	Passive Perception 13
Languages	Aquan
Challenge	6 (2, 300 XP)
Special 1	Hard Shell	After Cloyster uses Withdrawal,	it gains resistance to all damage until it takes another action
Special 2	Spikes	Whenever a creature hits Cloyster with a melee attack within 5 feet,	it takes 1d8 piercing damage
Special 3	Hold Breath	While out of water, the Cloyster can hold its breath for 1 hour
Special 4	Water Breathing	The Cloyster can breath only underwater
Special 5	Shell Armor	At the start of each of its turns,	the Cloyster deals 1d12 piercing damage
to any creature grappling it
Action 1	Multiattack	The Cloyster fires three Icicle Spears
Action 2	Tackle	Melee Weapon Attack	d20+5 to hit
Reach 5 ft, one target	Hit 1d8+2 bludgeoning damage
Action 3	Clamp	Melee Weapon Attack	d20+6 to hit
Reach 5 ft., one target	Hit 2d10+3 bludgeoning damage.	If the target is a creature,	it is grappled (escape DC 15).
Until this grapple ends, the target is restrained,	and the Cloyster can’t clamp another target
Action 4	Icicle Spear	Melee Weapon Attack	d20+6 to hit
Reach 5 ft., or range 40/60	Hit 1d6+3 piercing damage	plus 1d6 cold damage
Action 5	Spikes (2/day)	The Cloyster releases a burst of spiky shards of its shell on the ground in	a 30-foot cone.
Each creature in the area when the shards are scattered	must make a DC 13 Dexterity saving throw,	taking 2d12 piercing damage on a failed save	or half as much damage on a successful one.
Any creature that enters the area or moves through it	on its turn must succeed on a DC 15 Dexterity saving throw	or stop moving and take 1 piercing damage.	Until the creature regains at least 1 hit point,
its walking speed is reduced by 10 feet.	A creature moving throw the area a half speed	doesn’t need to make the saving throw
Action 6	Withdraw	The Cloyster withdraws its body into its hard shell and closes it tight.	Any creature that the Cloyster is grappling is released from
the grapple when it withdraws.	Until it emerges, it gains a +2 bonus to its AC,	it gains immunity to bludgeoning,	piercing and slashing damage from nonmagical attacks,
and it has advantage on Strength and Constitution saving throws,	While in its shell, it is prone,	its speed is 0 and can’t be increased,	it has disadvantage on Dexterity saving throws,
it is blinded and deafened,	it can’t take reactions,	and the only actions it can take are spikes	and a bonus action to emerge from its shell