For me, it was a trophy in Dead Space 2. It was called "Hard to the Core", and you had to play through the game with the enemies set to the hardest mode of the game, and you could only save three times the entire playthrough. The weapon I got for doing so was worth it.

I don't remember the name, but beating Halo Reach on legendary alone

beating dishonored without killing anyone

Dying on the first level.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Lol.

 

I guess beating any Pokemon game without using potions.......

One Who Has Proven Their Power in Persona 4 Golden which is to Defeat Margaret, shes not as bad as Elizabeth but still took some time, Original Gamer in Assassin's Creed 3 was hard to get as well, can't really think of any other ones, but some of the trophies I know that will be hard to get is AU/PT in Prototype which is to get Gold and Platinum in all the challenges, Hard to the Core in Dead Space 2 not really looking forward to that but do able, Adamant Will and Treasure Hunter in Final Fantasy XIII, Which name shall I use, in Naruto Shippuden Ultimate Ninja Storm 2 where you have to get all the tittles the only hard ones is getting 50 wins online but I'm getting closer, C'est Magnifique and Combo Crazy in Persona 4 Arena where you have to beat score attack with everyone and complete all the challenges for all characters, those are like really the only ones that I have trouble with and will be proud when I get them lol

Blazblue. "Hidden trophy," never got it.

Half Life 2: episode 1: 

"Shoot only one bullet during the game"

 

Well there is some work for Gravity Gun and Crowbar right there

Defeat Contra 1 without wasting any continue.

 

Or even worse, without losing a life.

 

THAT'S MANLY.

To me its beating Greenhill Zone in less then 1 minute in Sonic generations

Collecting all the Gold Skultullas in Ocarina of Time.

Definitely the Dead Space 2 "Hard to the Core" achievement. 

 

Seriously, you can only save three times the entire playthrough and If I recall, if you die once, you have to start all over. Mind you this is a game that averages at 9 hours to play with very difficult enemies and bosses. 

Duh the hardest achievement in any Video Game is getting all achievements.