SunnyBeam (Sunflora) @ Lum Berry 
Ability: Chlorophyll  
EVs: 52 HP / 248 SpA / 208 Spe 
Modest Nature
IVs: 2 Atk / 30 SpA / 30 Spe  
- Sunny Day  
- Solar Beam  
- Hidden Power [Fire] 
- Synthesis / Substitute / Grass Whistle

SpDef Wall (Sunflora) @ Leftovers  
Ability: Chlorophyll  
EVs: 244 HP / 220 SpD / 44 Spe  
Calm Nature  
IVs: 2 Atk / 30 Def  
- Leech Seed / Growth
- Razor Leaf / Giga Drain
- Hidden Power [Ice]  
- Synthesis  
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Optional Move(s): 
- Substitute
- Grass Whistle
Optional Item(s): 
- N/A
Optional Ability: 
- N/A
Optional EV/IV(s): 
- 52 HP / 248 SpA / 208 Spe (Timid Nature)
- 252 SpA / 4 SpD / 252 Spe (Modest Nature)
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Overview: Sunflora comes equipped with the highest base special attack in ADV ZU. This, in conjunction with its considerable special bulk and access to Leech Seed and Growth alongside reliable recovery in Synthesis, allows Sunflora to excel as a special wall. Sunflora is able to set itself apart from Lileep due to its pure Grass-typing, which allows it to resist Water- and Grass-types. It is also able to serve as a deadly sun sweeper with Chlorophyll and Solar Beam. This cements Sunflora as one of the premier rain team checks, as it can tank a hit, set up the sun, and win the matchup. 
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SunnyBeam: Sunflora is able to be used on sun teams thanks to its access to Chlorophyll and its immense Special Attack stat. This Sunflora runs Modest to have the extra power while still outspeeding fully invested base 85s like Staryu. These variants can be run alongside Chinchou to beat Elekid and Luvdisc, which are faster even with Chlorophyll active. Its HP investment hits a Leftovers number without hindering its Special Attack significantly. Sunny Day ensures Sunflora will get the Speed boost it needs. Solar Beam is Sunflora's strongest STAB and can be spammed while Sunny Day is active. Hidden Power [Fire] prevents Pokémon such as Bayleef, other Sunflora, or Magnemite from walling Sunflora. Synthesis provides Sunflora with a reliable form of recovery that gets a boost when Sunny Day is active. Substitute can be run to abuse Pokemon that might choose to switch out. Grass Whistle can also be used to put opposing Pokemon to sleep, but its accuracy makes it unreliable. 
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SpDef Wall: Leech Seed is used to chip switch-ins or as a form of recovery against bulkier Poison-type Pokemon such as Koffing, Grimer, and Dustox. Alternatively, Growth boosts Sunflora's already astounding special attack, which allows it to take advantage of Pokemon that cannot 2HKO it such as Elekid, Castform that lack attack investment, and Staryu. Razor Leaf lets Sunflora avoid becoming set-up fodder against Pokemon like Spoink and Delcatty thanks to its raised critical hit chance. Giga Drain can be run as another bonus recovery option, although Razor Leaf has significantly higher PP. Hidden Power [Ice] allows Sunflora to threaten other Grass-types such as Bayleef and Exeggcute while also threatening Pidgeotto and Taillow. Synthesis provides Sunflora with a reliable form of recovery. The given EV spread maximizes your HP while hitting a Leftovers number and allows you to outspeed uninvested base 35s like Clefairy and Koffing in the event you need to try and get chip on them before being knocked out. 
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Other Options: Sunflora can choose to run Timid on its SunnyBeam set, which allows it to outspeed Luvdisc and Elekid when Chlorophyll is active. This variant loses out on power, however.  A set with max investment in Special Attack and Speed with a Modest nature is one point faster in the sun than Elekid is naturally, so it could be considered, but you do lose out on a bit of bulk this way. 
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Checks and Counters: Status spreaders such as Butterfree, Magnemite, Lileep, and Dustox can hinder Sunflora's ability to act as a proper wall or to sweep. Physical wallbreakers such as Castform, Aipom, Taillow, and Pidgeotto can all overpower Sunflora with their STAB. Cyndaquil and Growlithe are able to wall Sunflora naturally as Fire-types and can 2HKO it with their STAB. Growlithe is worth noting due to it being able to use Sunflora as setup fodder. Grimer is also able to wall Sunflora and use it as setup fodder.