Side Deck cards are mostly alternate ideas for main deck options. Most likely 3x Swap Frog 1x Ronintoadin instead of the Mermails, or reduction of Unexpected Dai. One copy of Transmodify can be replaced with Downbeat if you want Transmodify to brick less, but Downbeat only works well on Retort Fusion/Roaring Ocean Snake into The Great Emperor Penguin unless you also run the frogs. I originally considered Genex Undine and Crystron Rosenix, but you cannot use Skull Dread or Link Spider or Genex Controller in the all WATER variant that Ice Barrier / Ice Knight / Silent Sea Nettle forces.
Foolish Burial Goods sends Ice Barrier which lets you send then retrieve The Great Emperor Penguin. Aqua Spirit, Ice Knight, Unexpected Dai, Mermail Abyssteus, Instant Fusion and Retort Fusion can provide a tribute for TGEP without using your normal summon.
TGEP goes into Glacial Beast Polar Penguin and Nopenguin, which make Penguin Brave (Polar Penguin will also banish a card on summon at this point due to Nopenguin). Penguin Brave sets Penguin Soldier or Nightmare Penguin from your deck which triggers Nopenguin to revive itself. With one additional monster you can use it and Nopenguin to make Marincess Coral Anemone, which revives a discarded Barrier Statue, or a material for Stealth Kragen, or Glacial Beast Polar Penguin to act as a tuner for another Synchro.
Penguin Brave can flip Penguin Soldier up on the opponent's turn, which will also trigger Nopenguin to revive again, so it's free to use Nopenguin as materials for something and not keep it around on your turn.
A decent common end board is Penguin Brave, Stealth Kragen, Penguin Soldier (set) and usually Marincess Coral Anemone or Mistar Boy, potentially with Barrier Statue of the Torrent, and Nopenguin auto-revíves when you trigger Brave. At minimum you have Penguin Brave Penguin Soldier and Stealth Kragen so that's at least 2 monsters banished and 1 destroyed -- with Barrier Statue and either Stealth Kragen or Penguin Brave on field you can sort of bottleneck a non-WATER opponent with only one summon that will get destroyed or banished.
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