Overview:
Believe it or not, Seadra can actually be a pretty good Pokemon to use on a team in PU. With decent base 85 speed, 95 special attack, and 95 defense, it has the capabilities to do well. The main problem with it, is that it just gets outclasssed by Floatzel in every way possible by being faster and having more attack. But even so, Seadra can still be used over Floatzel as it has more sets, and is slightly more defensive on the physical side. But, thanks to it's ability Sniper, it can become a crit machine, but in rare scenario.
All-Out Special Attacker:
Move 1: Scald/Hydro Pump
Move 2: Ice Beam/ Icy Wind
Move 3: Hidden Power Grass
Move 4: Flash Cannon/ Signal Beam
Item: Eviolite/ Choice Scarf
Ability: Sniper
Nature: Timid
EV Spread: 4 Def/252 SpA/252 Spe
Moves:
Hydro Pump is the Strongest STAB move that Seadra gets and does a lot of damage to those who take neutral damage. Scald has less power than Hydro Pump, but has more PP, more accuracy, and has a chance to burn the opponent. Ice Beam is for Grass-types such as Tropius and Meganium, who eat up Hydro Pump and Scald fairly well, and is also used for Dragon-types like Dragonair and Fraxure who resist Seadra's STAB. Icy Wind is also for these Pokemon, but can also be used to slow down set up Pokemon like Cherrim and Emolga. Hidden Power Grass is Seadra's only option for Water-types, such as Wailord and Floatzel since Seadra does not get Freeze-Dry. Flash Cannon can be used for Fairy-types with multiple coverage moves like Wigglytuff, Clefairy, and Floette. Signal beam is for Psychic-types, specifically Meowstic as it has access to Thunderbolt and outspeeds if Seadra does not hold Choice Scarf.
Set Details:
The 252 Speed EVs allow you to outspeed and hit strong base 80 and 85 speed attackers like Stoutland and Misdreavus. The 252 Special Attack EVs allow you to hit as hard as possible without the need for the Choice Specs. The Eviolite allows you to gain some decent bulk and occasionally lets you survive some super effective physical hits. The Choice Scarf is to allow you to outspeed Banded Floatzel, Raichu, Plusle and Minun, and Simisage and hit back with a strong attack. The ability Sniper is there to power up those rare but deadly critical hits. The Timid nature is simply so you can become faster, but can be replaced with the Modest nature if power is preferred over speed.
Usage Tips:
Switch in Seadra on a clean switch in to avoid taking damage. Then use each move on an opponent that it damages the most if holding Eviolite, or lock your self into the move that you best see fit if Choice Scarfed. If you have no super effective hits on the opponent, use your STAB. That's basically it. Just be careful on outspeeding Pokemon, or bulky Pokemon that can take hits.
Team Options:
Special walls are a huge problem for Seadra so strong physical attackers like Stoutland and Monferno are great team mates for Seadra. Hazard layers are always nice to have, so Pokemon like Gigalith and Golem are good Pokemon to use as well. And finally, Seadra's low special defense stat make it often times subject to special hits, so Pokemon like Mr. Mime and Probopass are excellent choices for special walls to have on your team.
Dragon Dance:
Move 1: Dragon Dance
Move 2: Waterfall
Move 3: Outrage
Move 4: Bounce/ Natural Gift
Item: Focus Sash/ Watmel Berry
Ability: Sniper
Nature: Adamant
EV Spread: 252 Atk/4 Def/252 Spe
Moves:
Dragon Dance is the main set up move here, as it boosts your Attack and Speed by one stage. Waterfall is Seadra's main physical STAB move and also has a chance to flinch. Outrage is to hit the Pokemon that resist the move Waterfall. However, it has a side effect of locking you into the move, so be cautious while using it. Bounce is for Grass-type Pokemon, but it is a 2 turn move so Pokemon with Protect can always stall it out. Natural Gift is also for Grass-types in conjunction with the Watmel Berry, however it's only a one time option unless Seadra has Recycle.
Set Details:
The max EVs in Attack allow Seadra to hit as hard as possible, since Seadra only has base 65 attack, in conjunction with the move Dragon Dance. The 252 in Speed are essentially for the same reason as the 252 in attack, which is to be as fast as possible without the need for the Choice Scarf. Having Sniper is basically for powering up critical hits like in the special Seadra set. Adamant nature is to hit as hard as possible due to Seadra's meh physical attack. The Focus Sash is to ensure that you get off one Dragon Dance and begin to at least try to take out the opponents Pokemon. The Watmel Berry turns the move Natural Gift into a 100 power Fire-type move, which can be more beneficial than Bounce, and can also throw off your opponent.
Usage Tips:
Make sure to switch in Seadra only on a clean switch in to avoid breaking the Focus Sash. Then immediately set up a Dragon Dance if you still have your Focus Sash. If not, just hit the opponent with strong physical attacks. After Dragon Dance is set up, begin to start attacking. Only use one Dragon Dance at first, since Seadra is not holding Eviolite and can't take hits that well. If more Dragon Dances are needed, choose to proper time to set up. And that's basically it. Use your STAB move if there is no type advantage on any other move.
Team Options:
Physical walls are a huge problem for Seadra so strong special attacking Pokemon such as Kadabra, Raichu, and Vanilluxe are great partners to have. Also special walls like Regice and Carbink are great to have since Seadra has pretty bad special defense and is not getting the boost from Eviolite. Other than that, use Seadra on a team that you see fit.
Other Options:
Since Seadra does not have the worlds greatest movepool, there aren't too many other options that you an utilize. On the Dragon Dance set, you could replace a move with Recycle in conjunction with a Lum Berry for Outrage, or a Watmel Berry for Natural Gift. Seadra can use Octazooka in replace of Scald or Hydro Pump, but the decrease in power just makes it seem not worth it. And finally, consider using Rest if you feel recovery is absolutely needed on either set.
Checks and Counters:
Special Attacks: Seadra has little Special Defense, so Pokemon with special moves force Seadra out, especially with Eviolite
Bellossom: Bellossom has good Physical and Special Defense which means it can eat a hit from Seadra, and then hit back with STAB Giga Drain.
Pikachu/Raichu: Both of these Electric-types can outspeed Seadra and hit it with a Thunderbolt if Seadra is not Choice Scarfed or has a Dragon Dance up.
