Klefki is definitely one of the more benevolent sort of tsukumogami.  Besides being pretty cute, in a weird keychainy sort of way, it even helps people by holding onto the keys to safes, a task with which it is trusted because it “never lets go of a key that it likes.”  Presumably you’d give these keys to your own Klefki, so that they’d still be on hand if you needed them, otherwise things could get awkward.  Wild Klefki?  Well, I suppose they collect lost keys, or are even ‘born’ with them – a lot of tsukumogami come to life after being lost or abandoned.  Or maybe they just steal them; fairies do that.  The other interesting thing about Klefki is that, if you look at the official art, or at its model in the game, it carries four keys, two of which look modern, while the other two look more like old-fashioned ward keys.  Who knows how long it’s been carrying those.  There’s no real-world comparison that would help us to guess how long an animated keychain might live, but if a key’s owner died without attempting to reclaim it then Klefki would probably hold onto the thing pretty much indefinitely.  I wonder whether it only gathers literal keys.  I’m now imagining a Klefki getting weighed down by all the metal keys it’s collected over the years, or just plain bored, and starting to learn and memorise passwords, or steal the bits of paper some people use to write theirs down.  In fact, I’m pretty sure the Pokémon universe’s version of LastPass is just one spectacularly high-level Klefki with an internet connection and nothing better to do.  Or, to move in the opposite direction, maybe some really old Klefki still lug around things like seal-stones and signet rings.  There are a lot of twists you could put on this Pokémon, if you were of such a mind.  It’s not a terribly interesting design as-is – I mean, it’s literally just “a living keychain,” what more can you say?  Once you accept that there’s nothing inherently wrong with a Pokémon that is basically a possessed or animated object, it’s hard to make a serious objection to it, but – like some of the least-interesting animal Pokémon out there – it’s just a cartoon version of something we all have in our real lives, which now has to compete for our affections with adorable magic dinosaurs and three-headed murder-dragons.  The creativity is in taking something that’s not normally alive and making it alive, which is a good start, but not necessarily much more than that.

  One final note: according to the Pokédex, Klefki “threaten any attackers by fiercely jingling their keys at them.”  Well.  I know what I’m trying next time I get attacked by a wild animal.

  Klefki’s defining feature as a fighter (aside from vicious jingling noises) has to be its ability.  Prankster is one of the loveliest things a support Pokémon can have; it lets you move first, ignoring speed, when using “status” moves – pretty much anything that doesn’t cause direct damage, which is a supporter’s stock in trade.  It also makes it much harder to screw over Klefki with Substitute or Taunt, which cause many or all (respectively) of your support moves to fail against a faster Pokémon (and Klefki is not fast).  A Pokémon with this ability lives and dies on its support movepool, since that’s what defines the types of horrible abuse it is able to commit against its enemies.  Like practically everything else, Klefki gets Substitute, and Prankster makes it very good at that; landing any sort of interference on Klefki can be difficult, and it’s also not an easy Pokémon to one-shot (especially with Fairy/Steel providing some lovely resistances).  To support your team, Klefki can set up Reflect and Light Screen to protect you and Spikes to damage enemies as they switch around.  It tends to be a little short of offensive presence, which is probably its biggest problem; it gets Thunder Wave, which is always neat, but anything that is immune or just doesn’t care that much about being paralysed is practically halfway to murdering Klefki, and its other offensive status moves are not a great selection.  There are worse Pokémon for using Toxic, though the same is not really true of Switcheroo; getting stuck with a Choice item by mistake would seriously ruin Klefki’s day, and it will generally value its own item – most likely either Leftovers or Light Clay – quite highly.  Then… I guess there’s Swagger, because Prankster and Prankstered Substitute do make it a pretty good Pokémon for confusion tactics, but it’s just kind of an obnoxious way to play Klefki since you’re basically amping up the luck factor and hoping things go your way, like using Double Team or Brightpowder.  Including actual attacks with this thing is sort of optional because it’s not terribly good at it, but if you want to, the Dark attack Foul Play uses the target’s attack stat in place of the user’s, making it is a decent way to ensure that Klefki can score solid hits against some Pokémon without diverting any effort away from training up its defences, though for obvious reasons many enemies will just shrug it off.  Most other attacks will be lacklustre at best since Klefki really does need to prioritise its defences, which are not that great naturally.  You could try a Calm Mind set with some combination of Flash Cannon, Dazzling Gleam and Psychic, but the fact is that Klefki’s just… not very good at that, compared to other Pokémon with Calm Mind.  Support is where its talents lie.

  There’s also a pair of interesting signature moves to talk about.  The first is Fairy Lock, which is one of those weird moves that don’t really look useful, but are.  It’s like Mean Look, Block, or Spider Web in that it stops its targets from switching out – except that it only lasts for one turn after you use it.  Pretty damning, you might think.  On the other hand, it affects all of Klefki’s opponents in doubles or triples, and it will still work even if Klefki is knocked out on the same turn (which would end a Mean Look effect), since Klefki is placing an enchantment on the battlefield, not maintaining a continuous effect itself… or something.  This means that your opponent is still trapped for one turn against whatever comes in to replace Klefki, and if that Pokémon is something that a) doesn’t feel particularly threatened by the trapped Pokémon, and b) can make effective use of a free set-up turn, then we have a recipe for fun times.  What’s more, thanks to Prankster, Fairy Lock is a priority move and relatively easy to slip in just before Klefki goes down.  The other signature move is Crafty Shield, and as far as I can tell this one is only useful in doubles and triples.  It’s like Quick Guard, Wide Guard, and Greninja’s Mat Block, in that it acts like a sort of Mass Protect, but with additional restrictions – in Crafty Shield’s case, it only blocks status moves.  On the other hand, unlike all the other moves of this class, Crafty Shield can be used repeatedly without incurring a chance of failure.  Taunt (which Klefki sadly does not learn) is probably still better, because it also stops status moves that are defensive in nature, and because you’re not going to be facing two support Pokémon at once all that often.  Crafty Shield is still an interesting little trick though, which pretty much sums up the way Game Freak have put this Pokémon together – it’s not great, but anything with Prankster is, almost by definition, going to be able to have a lot of fun with weird and clever support nonsense.