Magnificent Monsters

While you control a monster, except "Poseidra, the Storming Atlantean", your opponent's monsters cannot target this card for attacks. You can only use each of the following effects of "Poseidra, the Storming Atlantean" once per turn. You can send 1 other WATER monster from your hand or face-up field to the GY; Special Summon this card from your hand. If this card is Normal or Special Summoned: You can send 1 "Atlantean" or "Mermail" monster from your Deck to the GY, then target 1 card your opponent controls; return it to the hand.

Poseidra, the Storming Atlantean

2025 Mega-Pack Tin

(This card is always treated as an "Atlantean" card.)
You can discard 1 card to the GY; WATER monsters you currently control become Level 7 until the end of this turn. If this card is sent to the GY to activate a WATER monster's effect: Special Summon 1 Level 4 or lower "Atlantean" or "Mermail" monster from your Deck, except "Mermail Shadow Squad", also you cannot Special Summon from the Extra Deck for the rest of this turn, except WATER monsters. You can only use each effect of "Mermail Shadow Squad" once per turn.

Mermail Shadow Squad

Quarter Century Stampede

During your Main Phase, you can Normal Summon 1 Level 4 or lower Sea Serpent-Type monster in addition to your Normal Summon/Set. (You can only gain this effect once per turn.) When this card is sent to the Graveyard to activate a WATER monster's effect: Target 1 face-up card your opponent controls; destroy that target.

Atlantean Heavy Infantry

When this card inflicts battle damage to your opponent: You can Special Summon 1 Level 4 or lower "Atlantean" Sea Serpent-Type monster from your Deck, except "Atlantean Marksman". When this card is sent to the Graveyard to activate a WATER monster's effect: Target 1 Set card your opponent controls; destroy that target.

Atlantean Marksman

Quarter Century Bonanza

All Level 3 or lower Sea Serpent-Type monsters you control can attack your opponent directly. When this card is sent to the Graveyard to activate a WATER monster's effect: Add 1 Sea Serpent-Type monster from your Deck to your hand, except "Atlantean Dragoons".

Atlantean Dragoons

You can send 1 "Atlantean" monster from your Deck to the Graveyard, except "Neptabyss, the Atlantean Prince"; add 1 "Atlantean" card from your Deck to your hand, except "Neptabyss, the Atlantean Prince". If this card is sent to the Graveyard to activate a WATER monster's effect: Target 1 "Atlantean" monster in your Graveyard, except "Neptabyss, the Atlantean Prince"; Special Summon it. You can only use each effect of "Neptabyss, the Atlantean Prince" once per turn.

Neptabyss, the Atlantean Prince

Maximum Crisis: Special Edition

A ferocious serpent that was being hunted by Atlanteans. Battle-weary and ragged, it came upon an ancient light, and gained new strength for its battle. With its increased power, it launched an invasion of enemy territory with a renewed assault.

Phantasm Spiral Dragon

2014 Mega-Tin Mega Pack

You can Tribute this card and 1 Sea Serpent-Type monster; Special Summon 1 "Poseidra, the Atlantean Dragon" from your hand or Deck, then all monsters your opponent currently controls lose 300 ATK.

Legendary Atlantean Tridon

Battle Pack 3: Monster League

Target 3 Level 3 or lower Sea Serpent-Type monsters in your Graveyard; Special Summon all 3 of them. You cannot Special Summon any other monsters during the turn you activate this card.

Call of the Atlanteans

Realm of the Sea Emperor Structure Deck

This card gains 800 ATK while you control a face-up Fish, Sea Serpent, or Aqua-Type monster other than this card.

Atlantean Attack Squad

The Great Ocean Lord, who reigns over the depths, is served by these lancers. Deep-sea creatures exist in fear of facing the stream of attacks their lances are capable of.

Atlantean Pikeman

You can Tribute 3 Level 3 or lower WATER monsters; Special Summon this card from your hand or Graveyard. When you do: Return all Spell and Trap Cards on the field to the hand, and if you do, if 3 or more cards are returned to the hand by this effect, all monsters your opponent currently controls lose 300 ATK for each.