Like most Pokmon cards, the value of Klefki 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)
Mental Magic Much like Type Four, Mental Magic plays the game quite differently
My wait time spiked to over 6 hours
Ajani, Adversary of Tyrants fills out the cards at four mana
It also has relevant creature types in Zombie and possibly Knight, so there are other bonuses to be had depending on the build
Make sure to look over the entire Pokmon sets in order list to find other worthwhile cards before they also shoot up in price, or take a look at the best Pokmon packs for other cards you should attempt to chase