Like most Pokmon cards, the value of Seaking depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Aquapolis)
If you look closely at the 1st Edition version of this card, you'll notice an error
Meteor Strikes Double target creature's power and toughness until end of turn
Doubling Season , Branching Evolution , and Primal Vigor increase the number of +1/+1 counters placed on all of your creatures, which can make your Steelburr Champion and similar cards grow like crazy
Japanese Pokmon cards can be worth more when they have earlier releases, exclusive artwork, or better print quality
It was first printed on sorceries and instants, but also appeared in the Warhammer 40k Commander decks on three permanents, including Sister Repentia