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"Shark" (シャーク Shāku) is an archetype used by Reginald Kastle/Nash in the Yu-Gi-Oh! ZEXAL anime and manga. Most of them are Level 3 or 4 WATER and/or Fish. They are only supported as an archetype in the anime and manga.
The majority of "Shark" monsters, barring "Scrap Shark", "Shark Fortress" and "Corroding Shark", are WATER monsters. This offers them a healthy amount of support such as "Moray of Greed", "Sea Lord's Amulet" and "Salvage", on top of their swarming capabilities allowing for easy Xyz Summons of monsters with Ranks 3-5. However, this can also lead to them being vulnerable to overextending, so one should take care to not go overboard. Lower Level members such as "Hammer Shark", "Shark Stickers" and "Double Fin Shark" can reduce their own Level to Special Summon a Level 3 or lower WATER monster from the hand, Special Summon itself when a "Shark" monster is Normal Summoned and upon being Normal Summoned can bring back another one of your monsters from the GY, respectively. Some members like "Saber Shark" and "Double Shark" can manipulate the Levels of all monsters you control, adding to the versatility.
Some members also sport relatively high ATK values, allowing for some use for more than Xyz (and possibly Synchro) fodder, namely "Metabo-Shark" and "Scrap Shark". Though note the latter may not have the best synergy with other "Shark" monsters due to being a "Scrap" monster. Some members require Tributes to be Summoned, though they can easily help with the Xyz/Synchro Monster usage due to their Levels. A powerful member is "Hyper-Ancient Shark Megalodon", who pushes the aggressive style by destroying an opponent's monster when it inflicts battle damage, and "Sharkraken" can be Special Summoned by Tributing 1 WATER monster. Other higher Level members such as "Cyber Shark" and "Depth Shark" can be Normal Summoned without a Tribute, however. "Eagle Shark" and "Panther Shark" can be Normal Summoned without Tributes if your opponent controls 2 or more monsters, and can Special Summon themselves if you control the other. Note you can only control 1 each. "Shark Cruiser" can also 2 Level 4 or lower WATER monsters from the Deck when destroyed by an opposing card effect.
For the Extra Deck members, "Bahamut Shark" is able to use one of its Xyz Materials to Special Summon a Rank 3 or lower WATER monster from the Extra Deck, though it won't be able to attack the same turn the effect if used. As the effect is not a hard once per turn effect, it can be used multiple times a turn, however because the monsters aren't being summoned properly they can't be brought back from the GY if sent there. A good choice for this effect would be either "Number 47: Nightmare Shark" as it can attach any Level 3 WATER monster your hand or side of the Field to itself as material, or "Number 71: Rebarian Shark", who can act as a solid 2000 DEF monster. If "Rebarian Shark" is sent to the GY, it can then place any "Rank-Up-Magic" card onto the top of the Deck. This allows easy use of "Rank-Up-Magic - The Seventh One". If Summoned the correct way, "Rebarian Shark" can also revive and provide material for other "Number" monsters, using its own materials. This allows monsters such as "Number 101: Silent Honor ARK" and its "Number C" counterpart, "Number 94: Crystalzero" and its counterpart, and both versions of "Number 73: Abyss Splash" to be used as additional beatsticks. Another choice is both "Number 32: Shark Drake" and its evolved counterpart, as they can be Summoned quite easily. Base "Shark Drake" can attack multiple times and deal more damage after using its effect, but "Veiss" is more situational and possibly detrimental as it requires you to have 1000 LP or less to activate its effect and banishes resources from the GY. "Shark Fortress", while arguably a little trickier to Summon, can provide additional attacks without this downside and instead provides some protection by forcing the opponent to only battle it.
As some effects can only be activated when the monster is Normal Summoned, cards like "Double Summon" and "Water Hazard" become a must if one wishes to use them as much as possible. "Black Ray Lancer", its Full Armored and Rank 5 form and "Abyss Dweller" are excellent choices to use within a "Shark" strategy as well, the latter especially so as it can shut down the opponent's GY while providing a small ATK boost. "Beautunaful Princess" can also help immensely, as it allows to immediately use the effects of both "Buzzsaw Shark" and "Lantern Shark" who can easily Summon a Rank 5 monster. "Xyz Remora" and "Xyz Slidolphin" can also help with managing your Xyz Monsters. One may also consider using some cards from the "White" archetype, giving better access to Synchro plays and revival efffects; "White Howling" can help further shutdown the opponent's GY at the cost of simply controlling a WATER monster, denying access to any Spell/Trap effects that may activate there. Generic "Xyz" support could also prove to be invaluable.