Like most Pokmon cards, the value of Joltik 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 (Steam Siege)
Traditionally, it's quite normal for the newest Pokmon set to lose value in the first few weeks after release, as inflated preorder prices give way once the products can be bought off the shelves
Trainers must again participate in CPU battles and complete special challenges to earn rewards and packs that may contain the new card
Miscellaneous Sets (2001 2023) These other sets are sets that do not fit or have not been designed to fit into a certain sets release/series, and even though they release with similar artwork and Pokemon they are designed to be sub sets of their own nature.
My guess is that will be saved for a whole new set rather than a single booster pack, and that set will be released at the end of October
BATTLE You have your Commanders