Egg Beginner
Very Easy
Hatch a Pokémon Egg for the first time.
Egg Breeder
Easy
Hatch 10 Eggs or more.
Egg Elite
Medium
Hatch 50 Eggs or more.
Hatching Aficiando
Medium but “Time Consuming.”
Hatch 100 Eggs or more.
This is just more time consuming than actually hard. Many good Pokémon for Battle Subway or PWT usually have Egg moves, and often breed. Except for trading, you can not obtain eggs until you reach Route 3 Daycare. Having the Oval Charm may increase the rate Eggs that are produced.
those who are MM-ing will find this to be very easy, as even with the Shiny Charm it still can take more than 100 eggs for a shiny.
Archeology Lover
Medium
Have a Pokémon Fossil restored at the Nacrene Museum. The hard part is finding a Fossil, which a Man in Twist Mountain will give you one per day, after you beat the Champion.
Lenora gives us a fossil the first time you visit the Museum, and assuming we have an Antique Shop in our Join Avenue, we can get a fossil before we even reach the Victory Road. But yeah, the Museum, which is post-game, is still the only way to revive the fossils.
Pure Youth
Medium-Hard
Catch N's Pokémon.
http://serebii.net/black2white2/nspokemon.shtml REQUIRES MEMORY LINK WITH COMPLETED GAME?
Nope, obtaining N's Zorua (which does not require Memory Link and happens during the first visit to Driftveil) already lets you get the Medal. So it should be "very easy".
Pokérus Discoverer
Pure Chance
Catch a Pokémon infected with the Pokérus.
UNTESTED: Trading a Pokémon with Pokérus could give you this?
Yes, it can. I got Pokerus in my Black 2 game via trading an infected Pokemon from my Black game, and I received the Medal.
Castelia Boss
Easy?
Defeat the three Trainers on Back Street in Castelia City
Very easy, in fact. The only problem is that the area can only be accessed in Spring and Summer.
Wailord Watcher
Unknown
See a Wailord at the Marine Tube. (I may need Skitty for this one.)
LOL
By the way, you might want to put the time as well, it's 3PM-4PM.
Face Board Memorial
Unknown
Take a photo at the face board in Humilau City. (Not tested... Easy?)
Very easy, but iirc it can only be done post-game.
Ruins Raider
Medium
Reach the deepest part of the Abyssal Ruins.
More like "hard", might even be "very hard", since it's literally impossible without a guide.
Subway Top Gear
Medium
Reach a streak of 50 wins or more in the Battle Subway.
Runaway Express
Hard
Reach a streak of 100 wins or more in the Battle Subway.
should be "hard" and "very hard" respectively lol
OK Souvenir Getter
Easy
Receive 10 or more souvenirs from visitors in Join Avenue.
Good Souvenir Getter
Medium
Receive 30 or more souvenirs from visitors in Join Avenue.
Great Souvenir Getter
Hard
Receive 50 or more souvenirs from visitors in Join Avenue.
Tycoon of Souvenirs
Very hard
Receive 100 or more souvenirs from visitors in Join Avenue.
Receiving souvenirs seems to be luck-based, maybe you need to mention that.