Offensive (Staryu) @ Leftovers  
Ability: Natural Cure  
EVs: 252 SpA / 4 SpD / 252 Spe  
Timid Nature  
IVs: 0 Atk
- Rapid Spin / Recover  
- Hydro Pump / Surf  
- Thunderbolt  
- Ice Beam  

Bulky Spin (Staryu) @ Leftovers  
Ability: Natural Cure  
EVs: 252 HP / 4 SpD / 252 Spe 
Timid Nature  
IVs: 0 Atk  
- Rapid Spin  
- Surf  
- Thunderbolt / Ice Beam 
- Recover  
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Optional Move(s): 
- Hidden Power [Grass]
- Toxic
Optional Item(s): 
- N/A
Optional Ability: 
- N/A
Optional EV/IV(s): 
- 252 HP / 136 SpD / 120 Spe
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Overview: Access to Rapid Spin, a wide movepool, fantastic speed, and Natural Cure make Staryu shine in ADV ZU. 
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Offensive: Rapid Spin is run specifically for hazard removal but can be swapped with Recover to afford Staryu the extra longevity. Hydro Pump is Staryu's main STAB which is capable of threatening Pokémon such as Magnemite, Castform, and Aipom. Surf is an option that trades power for accuracy. Thunderbolt allows Staryu to hit Seaking, opposing Staryu, and Croconaw, while Ice Beam threatens Grass-types that may want to switch in such as Lileep and Bayleef. Max Speed with a Timid nature allows you to outpace key threats like Delibird, Pidgeotto, and Castform. 
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Bulky Spin: Bulky Spin uses Rapid Spin in tandem with Recover so that Staryu remains healthy after the chip damage from Spikes, as well as from prolonged damage throughout a match. STAB Surf allows Staryu to chip Pokémon as they come in on their own set of Spikes, and is its most reliable and consistent form of damage. Thunderbolt hits Pokémon like Seaking that may try to use Staryu as set up fodder. Ice beam on the other hand hits defensive threats such as Lileep. 
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Other Options: Staryu can opt to run an even bulkier spin set with 252 HP / 136 SpD / 120 speed. This allows Staryu to outspeed Seaking and avoid the 2HKO from Snorunt's Hidden Power [Grass]. Hidden Power [Grass] of its own is also an option over Thunderbolt to maintain a super effective hit against Water-types while being able to hit Chinchou, which has Volt Absorb and otherwise walls this set. Toxic is noteworthy, too, for being able to rack up damage against certain answers like Lileep, Bayleef, Sunflora, and Chinchou. 
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Checks and Counters: As stated above, Pokémon like Lileep, Bayleef, Sunflora, and Chinchou act as answers to Staryu. If Staryu lacks Ice Beam then Bayleef and Lileep are perfect Staryu switch-ins. If Staryu lacks Thunderbolt then Pokémon such as Seaking and Croconaw can use Staryu as set up fodder. Sunflora is unbothered by Staryu's Ice Beam and can 2HKO with Razor Leaf. Elekid is a noteworthy offensive check, as it outspeeds and OHKOs with STAB Thunderbolt.