Took a few tries but I beat him.
The Magneton fight kept dragging on since Watson kept healing him, and I had to use a several turns to heal both HP and Paralysis, so I got around this by using 2 X Attacks so I could finish Magneton off before he got into healing range.
With Magneton out of the way and with Sea God healthy and at +2 attack, Manectric went down easily.
This is proving to be easier than I thought. Seaking's movepool is garbage and its BST is nothing special and it's outclassed by pretty much every other Water type, but for in-game run purposes its stats are well-rounded and it only has two weaknesses so it can hold its own.
>>36691542That sounds nasty. At least other shitmons can grind. Did you basically just have to spam items?