Moves
Leech Life lets Araquanid act as a soft check to Pokemon like Latias and Hydreigon and regain some HP in the process. Lunge can be used over Leech Life as a Bug-type STAB move that prevents foes like Haxorus and Mega Altaria from setting up with Dragon Dance and punishes other physical attackers that try to switch in. However, the longevity Leech Life gives is generally much more valuable. Magic Coat is helpful to Araquanid when it's up against Pokemon that can reliably set up Stealth Rock on it or irritate it with Taunt or Toxic such as Swampert, Azelf, and Alomomola. Toxic can also be used over Magic Coat or even Leech Life because it's capable of bugging common Water-resistant Pokemon; however, most of them either can be muscled through with a STAB attack or rely on Toxic to beat Araquanid, making Magic Coat equally as efficient in that sense alone.
Set Details
Splash Plate heightens the absurd damage output Araquanid dishes out, increasing its ability to break opposing teams. This is often preferred over Focus Sash due to it being more effective in the long run, as Araquanid is not a suicide lead. However, Focus Sash can still be useful; even though Araquanid has decent bulk, Pokemon like Mega Aerodactyl, Terrakion, and Zeraora can otherwise OHKO it with a STAB attack, which would prevent it from setting up Sticky Web. This can be more valuable than Splash Plate during times where you just need to reliably get Sticky Web onto the field, especially in lead scenarios. 108 EVs in Speed allow Araquanid to outpace Blissey and everything slower than it. Araquanid can also viably run Waterium Z if there is no other Z-Move user on the team for a 160-Base Power Water Bubble-enhanced Hydro Vortex.
Usage Tips
Araquanid should primarily be used to set Sticky Web and irritate opposing teams with Liquidation and Magic Coat. You should get Sticky Web on the field as early as you reliably can so that your team, including Araquanid, can take advantage of it throughout the match. Even though Araquanid has decent defenses, switch it in sparingly. While it does resist the STAB attacks of Cobalion, Mamoswine, and Lucario, recklessly switching into these Pokemon could, along with Stealth Rock, deal enough damage to Araquanid to leave it unable to set up Sticky Web later on in the match. However, you can use Araquanid to soft check these threats in emergency situations. While getting Sticky Web up early is important, Araquanid is durable enough and forces enough switches to set them up throughout the match reliably, so you should keep it healthy if you feel you won't be able to keep your hazards up and will need to set them again later to win. Araquanid is capable of beating a lot of the more passive Pokemon in the tier due to its high damage output, immunity to burns, and access to Magic Coat. Magic Coat should be used to bounce back status moves such as Taunt, Stealth Rock, and Toxic. Bouncing back the latter is especially important to beat other bulky Water-types such as Alomomola. Also keep in mind that while you can bounce Stealth Rock and other hazards back, you cannot keep them off the field due to Magic Coat having fewer PP. Araquanid can be used as a soft check to Latias and Hydreigon thanks to its access to Leech Life and its high Special Defense stat. As said before, switch it in sparingly, but be aware of these matchups because their immunity to Sticky Web could thus make Araquanid vital to the rest of the team's success. Early-game, especially after setting Sticky Web, Araquanid can spam Liquidation to put dents in the enemy team. Liquidation has an absurd damage output due to Araquanid's ability and can do decent chunks to the majority of tier, including Water-resistant switch-ins such as Empoleon, Tsareena, and Latias. Pressure the opponent's hazard removal as much as you can because keeping your hazards up is vital to the team's success more often than not.
Team Options
Araquanid only fits on offense teams that appreciate Sticky Web support, as its niche is setting Sticky Web. Wallbreakers with a mediocre Speed tier appreciate Sticky Web support; some examples of this are Chandelure, Swords Dance Haxorus, and Mega Blastoise. Sticky Web teams have several matchup problems by default, the main one being non-grounded Pokemon such as Latias, Hydreigon, and Mega Aerodactyl. A good way to pressure these Pokemon is with priority; specifically, Scizor and Mamoswine pressure each of these examples with Bullet Punch and Ice Shard, respectively. Stealth Rock support is very necessary to help chip the opposing team down, particularly to punish Flying-type Pokemon that can ignore Sticky Web for coming onto the field. Stealth Rock setters that fit well on Sticky Web offense include Nidoking, Terrakion, and the aforementioned Mamoswine. These examples fit well because of the offensive pressure they give off, which makes removing hazards against them very difficult and lets them take advantage of the Sticky Web themselves. Bisharp can be a nuisance to deal with for Sticky Web teams due to its access to Defiant and priority, giving it a free +2 Attack boost once it comes onto the field with Sticky Web up. Pokemon that can deal with Bisharp while taking advantage of Sticky Web such as Lucario, Cobalion, and Infernape are appreciated. Moltres specifically is really difficult to handle due to its STAB combination and defensive typing in conjunction with its immunity to Sticky Web. Pokemon that can help pressure Moltres in conjunction with Stealth Rock that appreciate Sticky Web support like Nihilego, Latias, Quick Attack Scizor, and Zeraora can make a nice fit. Offensive Ghost-types that can spinblock foes such as Starmie, Tsareena, and Tentacruel can help keep Sticky Web on the field. Decidueye, Gengar, and Doublade are good examples of this. However, all of these examples fail to reliably block Rapid Spin due to most spinners' ability to offensively pressure them, making this appreciated, but not a necessity. Similarly, Bisharp also works very well with Araquanid due to its ability to deter and punish Defog users with Defiant, and it can also take advantage of Sticky Web in its own right. Bisharp also can pressure non-grounded Pokemon such as Mega Aerodactyl, Latias, and Moltres with Sucker Punch. More niche options that can take advantage of Sticky Web such as Choice Band Mienshao and Choice Band Darmanitan can also work due to their subpar Speed stats and absurdly high damage output.