Here is the full list of all 49 WWE '12 achievements worth 1,000 gamerscore. It takes around 25-30 hours to unlock all of the achievements on Xbox 360.
Create one arena in Create-An-Arena.
Use a movie created in Custom Entrance Video in an entrance scene (Single Player)
Create a story that includes a Custom Superstar or Custom Arena
Apply a Custom Logo to a Custom Superstar, Video, or Arena
Create a front, top rope and corner finishing move in Custom Finisher Move
Complete VILLAIN episode in ROAD TO WrestleMania (Single Player)
Complete OUTSIDER episode in ROAD TO WrestleMania (Single Player)
Complete HERO episode in ROAD TO WrestleMania (Single Player)
Use COMEBACK ability to increase momentum to MAX (Single Player)
Hold an Exhibition at a Custom Arena (Single Player)
Inflict heavy damage to opponent's head, arms, and legs (Single Player)
Win 20 times with submissions in one session (Single Player)
Win by applying a submission to a heavily damaged body part (Single Player)
Reverse an opponent's finishing move (Single Player)
Break 20 tables, ladders, or chairs in one session (Single Player)
Break 50 tables, ladders, or chairs in one session (Single Player)
Pin or submit Undertaker in the WrestleMania arena on Legend difficulty (Single Player)
Win at least once on Hard difficulty or higher (Single Player)
Win 20 times on Hard difficulty or higher in one session (Single Player)
Win 50 times on Hard difficulty or higher in one session (Single Player)
Win 37 times with Edge in one session (Single Player)
Win using a Custom Superstar in WWE UNIVERSE (Single Player)
Build momentum up to 75% in WWE UNIVERSE using a Custom Superstar (Single Player)
Build momentum up to 100% in WWE UNIVERSE using a Custom Superstar (Single Player)
Become #1 Contender for a Championship in WWE UNIVERSE using a Custom Superstar (Single Player)
Win one Championship title in WWE UNIVERSE using a Custom Superstar (Single Player)
Win 3 championship titles in WWE UNIVERSE using a Custom Superstar (Single Player)
Win 5 championship titles in WWE UNIVERSE using a Custom Superstar (Single Player)
Win or defend one Tag Team Championship in WWE UNIVERSE using a Custom Superstar (Single Player)
Win the Money In The Bank match in WWE UNIVERSE using a Custom Superstar (Single Player)
Cash in Money In The Bank in WWE UNIVERSE and win using a Custom Superstar (Single Player)
Injure an opponent in WWE UNIVERSE (Single Player)
Win a Royal Rumble match at Royal Rumble PPV in WWE UNIVERSE (Single Player)
As WWE UNIVERSE Royal Rumble winner, participate in the Royal Rumble Winner's Event
Win the final match at WWE UNIVERSE WrestleMania PPV (Single Player)
Win a Superstar match at the WWE UNIVERSE Draft Event (Single Player)
Interfere in an AI vs AI WWE UNIVERSE fight and beat one opponent (Single Player)
Interfere in an AI vs AI WWE UNIVERSE fight and beat all opponents (Single Player)
Play in an Xbox LIVE match (Player match/Ranked match)
Upload one creation to the WWE Community Creations
Content you uploaded to Community Creations is downloaded 5 or more times by other players
Review 5 or more items on Community Creations
Win a FREE BRAWL by throwing your opponent through the window (Single Player)
Create your own show in WWE Universe
Perform a Wake-Up taunt, hit your finisher, and then win via pinfall (Single Player)
Crawl to the ropes during a submission (Single Player)
Win a ONE ON THREE FREE BRAWL (Single Player)
Execute a Finisher against all 44 areas in FREE BRAWL (Single Player)
Use the limb targeting system to attack the same part 10 times in one match (Single Player)