The kingpin of the archetype, "Phantasm Spiral Dragon", is a retrained version of "Spiral Serpent". The flavor text of the former explains that the monster has survived through countless battles, which are shown in the artworks of the archetype's Spell/Trap Cards, displaying several instances of "Spiral" fighting the "Atlantean" and "Fire King" monsters. The names of the Trap Cards, all containing "whirlpool", reflect the attack of "Sea Serpent" described in its flavor text.
Spiral Serpent was an immensely powerful and destructive creature known for submerging entire cities with massive whirlpools. Among its victims were the original home of the Atlanteans and Lemuria, home of the Mermails. Spiral Serpent engaged in many fierce battles before eventually being defeated by the Atlanteans. However, this would not be the end of the beast. Spiral Serpent returned as Phantasm Spiral Dragon and engaged both Garunix and Poseidra who were deadlocked in battle.
Despite many of its Equip Spell Cards specifically summoning and attaching themselves to "Phantasm Spiral Dragon", it's far from the most important card in the deck; "Pacifis, the Phantasm City" is by far the most important card in the archetype's play style, practically requiring it be on the field to get plays going. Because it doubles as "Umi", it grants you access to "Sea Stealth Attack," a powerful Trap card that allows you to protect your other face-up Spell and Trap cards, like your aforementioned Equip Spells, or valuable stun cards like "Skill Drain" or "Soul Drain" that the deck's play style does not suffer from.
The "Phantasm Spiral Token" it summons can be kept on the field nearly constantly with attentive play, and can allow for unique plays like using it to pay the cost of "Sea Stealth Attack" or "Spiritual Water Art - Aoi" before immediately replacing itself, if those cards are chained to your opponent's effects. It also gives you access to "Champion's Vigilance", a Counter Trap every bit as powerful as "Solemn Judgment" without requiring a cost. As a Level 8 WATER monster, it also triggers the second effect of "Sea Stealth Attack", allowing the Token to crash into monsters it might not otherwise be able to defeat with its middling ATK.
"Pacifis" also searches out "Phantasm Spiral Power" and "Phantasm Spiral Battle", and allows you to activate them from your hand for spot destruction or negation, letting you surprise your opponent with traps without further cluttering your back row.
Due to all this, cards that can search out "Pacifis" or "Sea Stealth Attack" for you as soon as possible are key. "Terraforming" is a must, along with draw cards like "Card of Demise" or "Pot of Duality", whose costs barely concern the deck and its slow, deliberate play style. "Metaverse" is another decent option in most occasions due to its ability to activate or replace your destroyed "Pacifis" on your opponent's turn while serving as a backrow removal bait. While "Citadel Whale" seems perfectly suited to searching out "Sea Stealth Attack", the required conditions of "Power" and "Battle" require you not control any Effect Monsters to activate them. It does come with a monster targeting protection, however (something that the deck lacks). If properly timed, one could make a soft lock with indestructible backrow and monsters. The "Citadel Whale" may also be temporarily get rid of with Sea Stealth Attack's effect to make way for the archetypal traps.
The deck has some synergy with "Tenyi" cards, most especially the Main Deck Wyrm monsters designed to protect non-Effect Monsters on the field. "Tenyi Dragon - Manira" in particular offers further valuable protection for your monsters, and "The Hollow Cycle of Dragons" further incentivizes running "Mystery Shell Dragon" over "Megalosmasher X". While the "Tenyi" Extra Deck monsters are powerful, they don't count as Normal Monsters - only non-Effect Monsters. So they would interfere with the use of "Phantasm Spiral" card effects. Consider their inclusion (and by extension, "Supreme Tenyi-Style Fist") carefully. Or don't, and just play "Pot of Extravagance." In fact, do that anyway.
Because of the way "Pacifis, the Phantasm City" works, the deck stops functioning if your opponent does not activate any cards. Especially any build with few monsters in it may struggle to defend itself if your opponent's only actions are to Normal Summon a monster and attack. "Drowning Mirror Force" can be considered to slow your opponent down, but it can also become a dead draw any time the deck isn't experiencing this kind of simplistic opposition.
The deck is also dependent on its ability to draw and search cards, especially through the effect of "Pacifis", and so will lose to any card that prevents searching or stops draws; the likes of "Thunder King Rai-Oh", "Thunder Dragon Colossus", "Ash Blossom & Joyous Spring", and "Ghost Ogre & Snow Rabbit." Limiting searches with monster effects is less effective once the board is already set up, but can stop the deck cold in the early game. "Called by the Grave" can be considered to stop hand-trap monsters.
The deck also loses outright to non-destruction Spell and Trap removal, the likes of "Cosmic Cyclone", "Altergeist Meluseek", or "Evenly Matched." "Meluseek" can be stopped with "Skill Drain" or "Phantasm Spiral Power/Battle", but other threats may require "Imperial Iron Wall."
Monsters that cannot be targeted or otherwise outright immune to spell/trap effects also pose a threat to this deck (especially those with over 3400 attack) since you'll mostly rely on spell/trap cards for your disruption due to the deck's aversion to Effect Monster. Non-targetting removals such as the Mirror Force variants might be used to combat the former while the latter can be taken care of with battle, Kaiju effects, or cards that affects the player such as Gozen Match, Share the Pain, Ferret Flames.