Moves
Stealth Rock or Spikes is mandatory, giving Ferroseed the ability to utilize its above average bulk to set the entry hazard and support teammates. Gyro Ball is Ferroseed's main attack, taking advantage of its poor Speed stat in order to take on the likes of Mega Altaria and Mega Aerodactyl and discourage prominent threats such as Terrakion and Choice Scarf Hydreigon from directly switching in. Leech Seed is mandatory as Ferroseed's only form of recovery, allowing it to stay healthy over the course of long games. Toxic lets Ferroseed take on Celebi and Latias and also punishes common switch-ins such as Rotom-H, making it the best option in the majority of scenarios. Protect can be useful, however, to scout the likes of Choice Scarf Krookodile and Choice Band Terrakion and gain extra Leech Seed recovery.
Set Details
Eviolite is mandatory, giving Ferroseed the bulk it needs to take on metagame staples like Primarina. The given HP and Special Defense investment lets Ferroseed avoid a 4HKO from Choice Specs Primarina's Hydro Pump, with the remaining EVs placed into Defense in order to improve its survivability against weaker physical attackers. A Sassy nature and 0 Speed IVs provide the strongest possible Gyro Ball. Iron Barbs is Ferroseed's only ability, punishing common Rapid Spin users such as Starmie.
Usage Tips
Ferroseed's bulk and typing give it good matchups against threats like Primarina and Latias, forcing them to switch out. Use these switches as an opportunity to set entry hazards. However, before sending in Ferroseed, scout for coverage moves such as Hidden Power Fire on Latias and Fire Blast on Mega Altaria. The combination of Gyro Ball and Toxic is nearly mandatory for taking on the likes of Latias, Grassium Z Celebi, and Choice Specs Primarina, so prioritize landing Toxic on these threats before doing anything else. Protect should be used to scout out Knock Off and Trick users like Krookodile and Togekiss, which is important due to Ferroseed's reliance on Eviolite to check foes. It can also help Ferroseed scout for Choice item users with super effective coverage like Choice Scarf Infernape, as well as get a free turn of Leech Seed. Do not let Ferroseed stay in for too long, as its reliance on status moves for damage can often give openings to setup sweepers like Nasty Plot Infernape. If entry hazards are up, however, using Leech Seed is a semi-reliable option to recover HP while also chipping away at switch-ins. Still, Ferroseed's reliance on Leech Seed means one should focus on using it to check only one or two threats at most in order to avoid overstretching your limited resources and losing too much momentum. Lastly, Iron Barbs should be used to deter Rapid Spin as well as punishing weaker U-turns from foes like Gligar and defensive Celebi.
Team Options
Ferroseed fits best on bulky offense and balance teams looking for an entry hazard setter and answer to common threats like Choice Specs Primarina and Mega Altaria. Knock Off switch-ins are a necessity when using Ferroseed, so Fairy-types like Sylveon and defensive Primarina make for good partners. Sylveon and Florges in particular work well, as they can heal Ferroseed with Wish. Additionally, Heal Bell support from teammates such as Sylveon, Florges, Blissey, and Mega Altaria is helpful to keep Ferroseed healthy throughout a match. Fire- and Fighting-type checks such as Latias and Tentacruel are also necessities when using Ferroseed, as they can take on common switch-ins like Cobalion. Strong wallbreakers that can take advantage of entry hazards set by Ferroseed, like Nidoking, are good complements as well. Hydreigon in particular appreciates Ferroseed checking Fairy-types and Latias for it, making it a good option. Ghost-types like Mimikyu and Gengar can also take advantage of entry hazards while also blocking Rapid Spin from users Ferroseed cannot check safely, like Tentacruel. If using Spikes, an offensive Stealth Rock user is necessary in order to stop Defog and Rapid Spin users from removing entry hazards, as Ferroseed's lackluster matchups versus common removers like Empoleon, Mew, and Tentacruel mean it will struggle to keep Spikes up without support. Krookodile is a good example of this, as it can also use Taunt to prevent the use of Defog. Physical walls like Slowbro form defensive good cores with Ferroseed, as Ferroseed can deal with a lot of threatening special attackers that they cannot, like Primarina and Starmie. Checks to Scizor, like Tentacruel and Rotom-H, are good partners as well. Rock-types such as Terrakion and Rhyperior can take on Rotom-H and free up Ferroseed to run Spikes. Infernape is a very good teammate, taking advantage of the entry hazards set by Ferroseed, while Ferroseed can answer common checks to Infernape like Primarina and Latias.