Articuno @ Leftovers
Ability: Pressure
EVs: 24 HP / 252 SpA / 232 Spe
Timid Nature
- Roost
- Defog
- Hurricane
- Freeze-Dry
Well then, it's one of my first posts here too.
I chose Articuno for this matchmaking; despite Seaking has access to Lightning Rod, it has terrible defenses, and a weakness to Grass-Type which is pretty annoying, because there's a lot of mons with this type in PU (Leafeon, Roselia, Sawsbuck ...).
With its typing and pretty good bulk, Articuno will handle without problem Grass-type attacks, which could be troublesome for Seaking. Among that, Articuno will wipe out these mons with his STAbs Hurricane and Freeze-Dry, which will sweep away Water-Type mons. 232 Speed EVs and a Timid Nature allow to outspeed Jolly Gabite and Adamant Leafeon/Sawsbuck. Defog will be really useful, even if Articuno takes 49% of its health with Stealth Rock, Seaking doesn't have any recovery but Leftovers, and can be severely injured by entry hazards.
In the other hand, Seaking, thanks to the Water-Type resistances (even with its poor defenses), and Lightning Rod, can switch in mons like Rotom-Frost or Zebstrika, which could be a real pain for this bird. It can also handle Fire- and Steel-Type attacks, like Simisear's Fire Blast.