@ SPDShadowRanger - Marlon Joke:
Yes, that was one of the jokes I was debating to use.

@ Kwando7 - Pokerus:
Pokerus has always been around, it's just incredibly rare to get (it's a 3 in 65,536 chance of finding a Pokemon with Pokerus from either wild or breeding). However that is one of the medal I'm going to get because a year or so back I discovered my cousin had a few Pokemon infected with Pokerus (I'm assuming he caught a Pokemon with it, had it with him for a while so it infected the other Pokemon in his party, and then put it and a batch of them into his PC) so I traded one of his Pokemon over to my game and spread it to all my other Pokemon!

@ Kwando7 - Corless:
Because his Japanese name, Achroma, comes from "achromatic" which means "without color".

@ Medals:
Don't know how I feel about the Medals. On the one hand I like them as it gives you a few more things to do and you get a reward for doing them. On the other hand some of the challenges are either ridiculously simple that you wonder why it's even a challenge, ridiculously hard that I won't be doing them so they might as well not be there, or require you to like in Japan where within 1 mile radius your DS will pick up 1,000 other DSs with a good chunk of them playing Pokemon no matter where you go (in other words, the social Medals which I have no possible way of doing). But on the why-do-I-have-a-third-hand hand, being their only use it to decorate your Trainer Card with 1 of your Medals, I can't help but to see it as nothing to pay any attention to. With all this said I think I'm going to go through them summarizing them the best I can:

Special Medals:
All of these Medals are just congratulating you for collecting Medals, kind of pointless. The only two which makes sense here is the "Finishing Prize" which is a Medal for competing in a Rally and the "King of Medalist" which is for collecting all the medals (fat chance), but all the others seem just to be there to increase the number of Medals.
Adventure Medals:
"Step Medals": I guess we had to have some of these, however the only one which seems like a challenge is the last one, "Footprints of Honour", which is for 100,000 steps though even then that sounds small.
"Save Medals": Why is this here? You're awarding me for making sure everything I spent the last few hours doing isn't forgotten? I mean if these Medals didn't exist is there someone out there who's going to say "Well if I'm not getting a Medal for this then why bother?". Also what's stopping someone from just spending half an hour saving over and over again until they get all of them? Do you have to play your game for a certain length of time before it's accepted as a "new save"? Probably not.
PokeCen Fan: Once again, you're awarding me for something I'm naturally going to do throughout the game. And like before, what's stopping me from spamming healing, unless you programmed the Nurse to actually refuse healing if you're Pokemon are at full health (and even then you'd just have to hurt them a bit in a wild battle for her to heal them again).
"Sign Medals": Hm, I guess this would be okay if it wasn't so simple. Not everyone bother to read the signs so it's actually something you have to go out of your way for. However I would prefer the challenge to be something like "read all the signs on every route", "read all the signs in every city/town", "read all the signs in Unova", etc.. However the "Graffiti Clairvoyance" sounds interesting as I never knew some signs had graffiti on them (hopefully it's only a small few signs that have graffiti and not all of them since that would kind of ruin the success of finding one with graffiti).
"Bike Medals": Like the "Step Medals", I suppose we had to have one of these too. However this has the same problem as a lot of the others above have as you just need to "ride your bike" to get these though unless there's a # of steps you need to ride for it to count what's stopping someone from spending half an hour getting on and off and on their bikes?
"Super Rod Medals": Being you just need to "use" the Super Rod this is another throw away one. If it required you to hook and catch a Pokemon I would say these medals actually give you a "challenge" (still an easy challenge, but a challenge), but since they don't just spend half an hour spamming the Super Rod.
"Capture Medals": This is more like what I'm thinking these medals should be but in a bland sort of way. Each one is just catching all of that type in the Unova Pokedex except for the last two. Why not have one which requires you to "capture all the version exclusive Pokemon" or "capture all the form differences of the Pokemon with them in the Unova Dex". Also the last two, "Unova Collector" and "International Collector", which requires you to catch all the Pokemon in Unova Dex and then in the National Dex, have the SAME MEDAL DESIGN as each other and the Medals which just require you to catch all of a single type in the Unova Dex!
"Box Medals": Once again, this is awarding us for doing something which we normally do. However they could have gotten a bit fancy here like requiring us to put certain Pokemon in boxes like "have a box contain 1 of each type of Pokemon" or "make the Pokemon in a box form a shape of a heart". The last one, "Box Max" which is filling all the boxes with Pokemon, is the only one which I think deserves to be here as they are right now.
Capture King: 50 Pokemon in one day? Sure, but that'll be a lot of level 2-5 Pidoves, Patrats, and Lillipups...
"Vendor Medals": Only interesting one is the "One More Drink" which you get for getting a free drink from the Vending Machine... is this a new thing in the game?
"Evolve Medals": Read "Box Medals". They could have some like "Don't evolve a Pokemon until it learned every move it can via leveling up" or "Evolve a Pokemon just when it reaches level 100".
"HM Medals": It's not even all the HMs, just Fly and Strength, what's the point? And you only need to use them just once. Is it so much to ask for some creativity?
Search Master: Look in a bin once... do we need to find anything? If we need to find something and only a very few bins have something then like the graffiti one I would consider this a bit of a challenge... but as they wrote it I think you just need to look in a bin ONLY ONCE.
"Lost Property Medals": Like the ones similar to it, the last one is the only one which I would consider a challenge. Though the Dowsing MCHN does pretty much make getting these a piece of cake.
Naming King: I'm assuming the Pokemon already needed to have a nickname? Fine, change it to get the Medal, and then change it back. It was if there was no point.
TV Addict: Oh, we can finally change the TV channels, maybe I could find one which doesn't have creepy people who seem to know EVERYTHING ABOUT ME.
"PokeMart Medals": For the money spending ones, only the last two, "Luxury Special" and "Super Millionaire", seems like it'll be an interesting challenge. "Skilled Shopper" is a rather fun way of showing that buying 10 normal Pokeballs get you a Premier Ball, however considering it's the PokeMart thus having various items for sale they could have done more things. Maybe even include something involving Shopping Mall Nine.
Sweet Home: This medal is rather far done the list for one which you'll most likely get in your first batch of Medals in the game considering your home city is WHERE THE FIRST GYM IS.
"StreetPass & Pass Power Medals": Remember that Japanese joke I made? Well here it is in full glory. As I said, I'll probably be getting none of these. Well, maybe the "First StreetPass" and "Pass Power+" if my cousin gets the game, but at most that's what I'll be getting with these.
"Dream World Medals": Hey, something involving the Entralink I CAN get! As for worthy of being challenge I'd say the last one, "Let's Meet in a Dream" for transferring over 100 Pokemon. Though they could have done some more things, especially since the Dream World also provide you with items.
Hidden Hole Expert: Hey, one that does sound like a challenge. I would say they could have done more but I've said that already for a lot of them.
"Egg Medals": Remember those "Step Medals" and "Bike Medals"? If you don't want to be cheap then I suppose getting these Medals will help get those other two groups Medals if you don't have them all already. Speaking of which I'm adding the "Day-Care Center Mania" one here since if you're doing these you'll get that one easily.
Fossil Master: For this one I'm stuck between thinking "you're being awarded for something you normally do" and "you do have to go out of your way to do it". Though being you just need to do it one time I sadly have to learn toward the former thought.
Pure & Innocent: Ah, some explaining here. For those who don't know, using something called "Memory Link" which involves your Black and/or White version, at Chargestone Cave you'll get a vision of N releasing the Pokemon he used to battle you in those games back into the wild. After the vision you'll then be able to encounter these Pokemon in the wild. While these Pokemon looks and has the stat or a normal Pokemon of its species, will actually sparkle like a Shiny Pokemon upon entering battle (also upon encountering one in the wild a message saying it may not be wild appears, the Pokemon's OT (Original Trainer) is "N", have an ID of "00002", and you can't nickname/rename them). So yeah, I guess this is an interesting challenge (as long as one of the Sage's giving you N's Zorua doesn't count), though they could have had a series of Medals involving N's Pokemon like "Catch all of N's Pokemon", "Beat the Elite Four & Champion with a team of N's Pokemon", "Fully evolve all of N's Pokemon that can", or "Train all of N's Pokemon up to Level 100".
Lucky Colour: This Medal probably would mean more if it wasn't for the fact that after completing the Unova Dex you can encounter a Shiny Haxorus...
Pokerus Hunter: Though this one still retains its challenge... if you don't already have Pokerus infected Pokemon in your Black and/or White version that is.
Castelia Gang Leader: Now is defeating the Castelia City gang a required thing to do or an optional. If it's optional then I'll accept it as a challenge but it it's required then once again you're being awarded for something you're suppose to do anyway.
Railway Mania: Being a different train is on display each day I suppose this could take a few days to complete (more if you miss a day) if you don't want to go through the hassle of changing your DS's clock.
Wailord Watch: How rare is it to see a Wailord in the Marine Tube? Also do you have to do something for one to appear or can you, say, leave your DS on (and plugged in) and go off to do something else and eventually (and hopefully) one will randomly appear while your away so that when you get back you can go get the Medal?
Appearance Memorial: Once again, being it sounds like this is the only place you can get a photo and you need to do this only once it's not really a challenge. It could at least require you to have a Frillish in your party...
Heavy Machinery Mania: Hm, this sounds like an interesting challenge, actually it sounds like one you may even need a guide for!
Ruins Master: Another one which you'll probably need a guide for, wow, why is it now they're getting good? Though I wonder if they kept continuity and have it be empty since I don't know anyone who wouldn't have cleared it out though then again it does seem that canonically your character actually didn't do some of the things you probably did in Black & White.
Diamond Dust: If it wasn't for the fact that on Junichi Masuda's birthday (January 12) that Diamond Dust appears in Icirrus City, this would have been difficult to get.
Bridge Mania: *Sigh* Though I know for main story you don't (or rather can't) do this, it's very likely you'll keep playing for the post story which would require you to cross every Bridge, thus making this Medal being one which rewards you for doing something you have to do anyway.
Unova Revolution: Same as "Bridge Mania" above, if you're playing post story you're going to do this anyway.
Adventure King: Okay, it's the obligatory "Series Finished!" Medal, can't argue anything here.

AND I think I'll stop here for now. I'll go through the rest the next following days.