Sun Setter (Onix) @ Salac Berry  
Ability: Rock Head  
EVs: 200 HP / 56 Atk / 252 Spe  
Jolly Nature  
- Sunny Day  
- Explosion      
- Endure
- Earthquake
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Optional Move(s):
- Block
- Taunt
- Rock Slide
- Rock Tomb
- Double-Edge
Optional Item(s):
- Choice Band
Optional Ability:
- N/A
Optional EV/IV(s):
- 4 HP / 252 Atk / 252 Spe
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Overview: Access to Sunny Day, Endure and Explosion, combined with decent Speed and good physical bulk, allow Onix to function as a solid Sun setter, though it struggles to find any use outside of this niche.
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Sun Setter: Sunny Day allows Onix to set up Sun, activating Chlorophyll for sweepers such as Sunflora and Nuzleaf, while powering up the Fire STAB of wallbreakers such as Castform and Growlithe. Explosion allows Onix to get off the field as fast as possible, as well as threaten heavy damage on most Pokemon that don't resist Normal. Endure + Salac Berry allow Onix to get off Sunny Day against threats who would otherwise outspeed and KO Onix before it could move. Finally, Earthquake allows Onix to beat certain threats such as Grimer 1v1, while denying Normal resists such as Rhyhorn the opportunity to setup. This EV spread maximizes Speed while giving Onix enough physical bulk to survive 2 Brick Breaks from Choice Band Aipom without needing Endure, while the remaining EVs are dumped into Attack to maximize the power of Explosion and Earthquake.
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Other Options: Block could be used to trap favorable matchups such as Grimer, though most would switch out immediately against Onix anyways. Taunt could be used to try to deny setup, notably Spikes from Snorunt. Onix could run a Choice Band set with Earthquake, Rock Slide, Double-Edge and Explosion, with maximum Attack and Speed investment, though it suffers from a severe lack of power.
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Checks and Counters: Most Pokemon can easily 1v1 Onix if they aren't weak to Earthquake, but they must be weary of Onix attempting to trade using Explosion, which can usually only be tanked by Pokemon that resist Normal such as Lileep. However, Onix's fundamental goal is almost always to set up Sun and then Explode, which can only realistically be denied by faster Taunt users such as Aipom, Quick Attack users that can outspeed and OHKO Onix such as Elekid, or a weather sweeper whose boosted speed lets it outspeed +1 Onix such as Seaking in Rain.
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