Talked about it last night on the Orange Island IRC channel so I was able to collect most of my thoughts there. Now that we know its legit:
Tapu Koko:
So is that its actual name? If so that's interesting and it's not like any naming convention we had before. I suppose for a group of Legendaries we can make this exception, also help to show its Legendary status of having a more name-like, well, name than a species.
Design wise a bit of a complicated design, though at the same time fits the "guardian" appearance. Obviously has a bird theme (specifically chicken/rooster) to it (we'll get to typing), its having a shield or shell of some kind that can be combined to look like a bird-lik face. Neat, will the other Guardians have such a gimmick (was talked about in the Orange Island IRC channel maybe they'll have a sort of totem theme going on, Tapu Koko being the head while the others are the body, arms, and legs).
Typing is Electric/Fairy. Well already this sort of breaks the alchemy theory a bit, especially with the idea that Melemele Island's Guardian is of Water (I suppose it could be Air and the Mountain Island one is of water if they make it having to do with ice). However it's a cool typing that's only been done once by a lackluster Pikaclone so excited to see what a Legendary could do with it. That all said, a Fairy Legendary. It begins folk. I don't want Fairy to become the new dragon where a whole ton of Legendaries are part Fairy-type. I get it, fairies are legendary creatures so it's logical to base Legendaries on them. Except Tapu Koko doesn't look like a Fairy-like creature, at best it looks like a spirit (though wouldn't it be Ghost in that case?). Hopefully the other islands will have their Guardians be different types (maybe Dragon and Ghost to get all the mythical types).
Elekimaker is an interesting Ability, one that activates a field effect automatically! Imagine there being one that lets you do this for the Rooms like Trick Room? Also nice to see they aren't abandoning Terrain moves like they've done with other series of moves. If the Guardians have similar Abilities we'll most likely be getting a few more. Though now I'm on the watch to see if Tapu Koko gets Rest or a sleep inducing move. :P
Its Signatrue Move is "Wrath of Nature", sounds like it would be powerful though doesn't sound Electric-type. Fairy-type, maybe? *sigh*
Hm, Hala is using it. I guess on occasion the Guardian may let the strongest trainer on the island use it if they want to battle?
BTW, in the intrductory video, did Tapu Koko just vaporize those Spearow? O_o
Charjabug & Vokavolt:
Obviously Grubbin's evolutions. And as guessed by the majority, it evolves into a Bug/Electric.
But as I predicted, Charjabug looks to be based on the pupa stage of beetles. Also it looks to be designed after a battery pack (hinted by its Japanese name) or generator? And it does have a snazzy pair of shades.
Vikavolt is able to fly yet is Bug/Electric. So either it has Levitate (which would help distinguish it from the Joltic line) or needs another Ability to help it stand out (its Japanese name hints of it being ome kind of gun or cannon, maybe give it Mega Launcher with an Electric-type pulse move?). As I said, if this is a gen bug it's coming off the heels of Vivillon so needs something to not look like a step back. Anyway it looks cool with those jumper cable clamps mandibles.
Drampa:
Well let's get this joke out of the way.
Wait, Normal/Dragon? Well it's nice to see a new type combination (and oddly another one where Normal is first), but for Drampa? It looks either Water/Dragon or Flying/Dragon depending on how you see its design (unless its suppose to be both thus why Normal so it can fly and swim. Hmm, imagine if this thing becomes the ultimate HM slave learning Fly, the Water HMs, and maybe the othe HMs as well). To me it looks like a dragon figurehead (especially with the blank eyes), like CAP's Naviathan. However I am now seeing maybe some airy design, like the sea form could be interpreted as clouds.
Frenzy increases Special Attack by two stages. In the vid it was attacked with a Super Effective attack and brought down to red HP, so the increase is either from getting hit by a Super Effective attack or falling below a certain amount of HP. If Drampa can heal I could see potential in this (and if Drampa's stats are also good enough which is debatable. A random dragon that's very likely not the psuedo-Legendary, I'm getting Druddigon vibes here).
Also one thing talked about in the Orange Island IRC channel, brought up by
DHR-107, is could this thing be a Lapras expy? Certinaly looks like it could be, though being Normal/Dragon I'm now doubting it. Could be wrong, and I brought up since Alola will probably have a bit of Surfing to it maybe they'll be introducing more water transport Pokemon (would be nice to have more Pokemon have their model on the overworld... which would be easier to do now that they're using the in-battle models on the overworld).
Bruxish:
... This thing looks terrifying. It seems to be based on the Reef Triggerfish (Hawaii's official fish, thank you DHR-107) and a Filefish (thank you Bulbapedia). Very colorful, though you're probably wondering whu it was combined with a teeth grinding disorder (bruxism). Well it just so happens those two species of fish have teeth and do use them to eat.
Though not sure if it'll help it much, being Water/Psychic it sounds like a Special attacker unless they make it a mix which will probably be more of a detriment then help.
However its Ability, Dazzle/Vibrant Body, might be useful in the metagame. It blocks priority moves, shown when block Kangaskhan's Fake Out or, in the leak video, Pikachu's Quick Attack. Could it (and Stakeout) be moves that revolutionize the metagame or will they be stuck on mons who stats can't really bring out these moves full potential?
Cutiefly:
Based on a Bee Fly, specifically the Bombylius Major, as its name applies its cute. Surprised they released another bug in the same announcement as Grubbin's evolutions, though it being Bug/Fairy does stand it apart.
However, just like when Grubbin was released, there's nothing really to say about it right now. It just is.
Togedemaru:
I question whether this will be its English name. Now for the Pikaclones they usually try to keep aspects of it Japanese name, but still this is a mouthful for an English speaker (especially for a child).
Originally thought a porcupine or hedgehog Pikaclone, it's name reveals it to be based on the Ryukyu Spiny Rat (who's Japanese name is "Togenezumi"). Alright, gives it a "spike" gimmick.
Oh, and its Electric/Steel, so maybe there's also a mace theme to it? Not sure what the Steel-typing will do for it (besides quad weak to Ground).
Lightning Rod is alright if generic, and it gets a new move called "Discharge Strike" which looks... like a Special Electric-typ move. Going to need to know more about it.
Zygardes 50%*2=Perfect:
Zygardes 50% confirmed to not only have access to its other Signature Moves but also will be able to have the Swarm Change Ability. Interesting, I guess there will be a way to change out its Ability (and if that's true maybe 10% may have a different Ability of its own)? Though now this presents a question: Why use 10% over 50%?
That's all my thoughts for now. Time to go through the comments and like/respond.