"Penguin" (Japanese: ペンギン Pengin) is an archetype comprised of WATER monsters used by Crump and Rio Kastle in the anime. Most of the "Penguin" monsters have unremarkable ATK and DEF, instead focusing on bouncing effects to disrupt the opponent's field, and Special Summoning "Penguin" monsters from the Main Deck and Graveyard. Some of the Effect Monsters are quite splashable, such as "Penguin Soldier" and "Nightmare Penguin".
"Penguin Soldier": Can return up to 2 monsters on the field to the hand, including itself if it wasn't destroyed by battle when flipped (such as when Flip Summoning itself). Especially effective against Synchro, Fusion and Xyz Monsters, since they go back to the Extra Deck, which means the opponent loses field advantage without gaining hand advantage. Since the cards are returned to the hand, this is useful to remove monsters when effects make destroying them difficult, such as "Legendary Six Samurai - Shi En" and "Stardust Dragon".
"Penguin Knight": Being the first Penguin Effect Monster printed, it's effect is far different from the others in the archetype. Being a very situational re-shuffle effect, somewhat similar to that of "Fiber Jar" but that has to be initiated by your opponent, it is really questionable as whether or not to use it in a typical Penguin deck. However, using it in combination with "Nopenguin", if this card's effect is activated while you have a "Nopenguin" in your Graveyard, all the cards in your Graveyard will get back to the Main Deck, but a monster will be Special Summoned in the opponent's turn, giving you a double line defense.
"Nightmare Penguin": Much like "Penguin Soldier", this card can bounce many of your opponent's stronger monsters. This card can only target 1 card, but it has a basic 1800 DEF, and might withstand an attack which "Penguin Soldier" may not. It is also Level 4, which makes it a perfect target for "The Great Emperor Penguin".
"The Great Emperor Penguin": Can be Tributed to Special Summon up to 2 other "Penguin" monsters from your Deck. With its effect, many power-plays are enabled, and therefore it is currently considered the "Penguin" Deck's strongest card. Its effect can be combined with "Lemuria, the Forgotten City" to raise the levels of the Summoned monsters to Xyz Summon Xyz Monsters with higher ranks.
"Nopenguin": Useful for Rank 3 Xyz Summons, because it Special Summons itself from the Graveyard whenever the effect of a "Penguin" monster is activated, but only once per turn. While it can only be Summoned with its effect once per turn, Special Summoning it each turn is still useful each turn, as long as you have "Penguin" effects to activate. In addition, it banishes monsters that are returned to the hand by "Penguin Soldier" and "Nightmare Penguin".
"Penguins" focus on bouncing cards back to its owner's hand with cards like "Penguin Soldier" and "Nightmare Penguin". Cards like "Neo-Spacian Grand Mole" can be used in this Deck to keep with the bouncing theme. You can also use "Nopenguin" or "Degenerate Circuit" to banish bounced cards instead of returning them to the hand. "Spiritual Water Art - Aoi" can dispose of monsters that you returned to the opponent's hand, so using it after using "Penguin Soldier" or "Nightmare Penguin" is a great combo to get rid of strong monsters. By using "Book of Moon", you can re-use these effects to return cards to the opponent's hand again.
"Monarchs" can be used to fill out the Deck, since you often have an extra "Penguin" available for Tribute Summons.
“Fluffal Penguin”, despite also being a member of this archetype, has little synergy with the rest of the members because it’s primarily meant to support “Fluffal” cards, that and being a “Fairy” monster makes it a little awkward to include in a dedicated Penguin deck (though it is still appropriately WATER type).
Due to the new mechanic of Link Monster cards, spamming Xyz monsters is not as easily done anymore, especially in this deck, so including some generic Link monsters like “Mistar Boy” would be helpful.