Hidden Arsenal: Chapter 1

"Deep Sea Diva" + 1+ non-Tuner monsters
Once per turn (Quick Effect): You can discard 1 Level 4 or lower WATER monster; this card gains 800 ATK until the end of this turn. If this Synchro Summoned card is sent to your GY: You can target 1 Level 5 or higher WATER monster in your GY, except "Deep Sea Repetiteur"; Special Summon it in Defense Position, also you cannot Special Summon monsters for the rest of this turn, except WATER monsters. You can only use this effect of "Deep Sea Repetiteur" once per turn.

Deep Sea Repetiteur

2021 Tin of Ancient Battles

If this card is added from the Deck or GY to your hand by an effect of a WATER monster: You can reveal this card; look at your opponent's hand. If this card is Special Summoned: You can send the top card of your Deck to the GY, then target 1 Level 4 or lower WATER monster in your GY, except "Deep Sea Artisan"; Special Summon it, but negate its effects. You can only use each effect of "Deep Sea Artisan" once per turn.

Deep Sea Artisan

You can discard this card and 1 WATER monster; look at your opponent's hand and banish 1 card from their hand face-up, until the End Phase. If this card is Special Summoned: You can send the top 3 cards of your Deck to the GY, then target 1 Level 4 or lower WATER monster in your GY, except "Deep Sea Minstrel"; place it on the top or bottom of the Deck. You can only use each effect of "Deep Sea Minstrel" once per turn.

Deep Sea Minstrel

If this card is sent to the GY to activate a WATER monster's effect: You can make your opponent banish 1 card from their hand face-up, until the End Phase. If this card is Special Summoned: You can send the top 2 cards of your Deck to the GY, then target 1 Level 4 or lower WATER monster in your GY, except "Deep Sea Sentry"; add it to your hand. You can only use each effect of "Deep Sea Sentry" once per turn.