The Pokmon TCG archetype that will suffer most against Klefki is Lost Zone Box
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The biggest knock against Unsettled Mariner is the fact that it is likely difficult to find room for multiple copies, but the ability to protect your creatures (and yourself) from spells your opponents cast is potentially quite valuable
Kefka takes things a bit further by giving you access to black in your deck, though, giving you access to creature reanimation and tutoring straight for a Niv-Mizzet to combo out quickly
Notably, Arcanine exs Raging Claws attack, which only requires two Fire-type energy, scales with the number of damage counters on Arcanine ex, meaning the maximum damage it can do is 300 a whopping amount for only two energies
As for Suicunes damage potential, it will really depend on the development of the game