These hidden missions can be found in the Plutus and Cacus systems. In the Plutus system of the Hades Gamma Cluster get 75% Renegade and in the Cacus system get 75% Paragon.

To unlock two gamer pics that can be used on your profile complete the game on the Hardcore or Insanity difficulty settings gaining the indicated achievement.

Unlock Saren Gamer Pic:
Gain the 'Distinguished Combat Medal' achievement.

Unlock 'N7' Gamer Pic:
Gain the 'Medal of Valor' achievement.

When you beat the game using a specific class you can give the corresponding 'Bonus Talent' you recieve to a new character you create.

Adept Class:
Singularity

Vanguard Class:
Shotgun

Infiltrator Class:
Sniper Rifle

When you complete the game on the 'Normal' difficulty setting with the following requirements the indicated bonus feature can be unlocked.

Hardcore Mode:
Complete the game once.

Unlock Insane Difficulty:
Without changing the difficulty setting beat the game on the Hardcore difficulty.

Increased Level Cap (51 - 60):
Complete the game once.

Unlock New Game +:
When you complete the game the 'New Game +' feature will become unlocked where if you select 'Existing Career' you will retain your character and any equipment and skills you earned previously.

When you complete the following tasks in the game the next time you start a new game the corresponding bonus is unlocked.

Unlock +10% Experience Bonus:
Complete 75% of the Game.

Unlock +10% Hardening Bonus:
With Ashley in the squad complete 75% of the Game.

Unlock +10% Health Bonus:
Kill 150 Organic enemies.

Unlock +10% Shield Bonus:
Kill 250 Synthetics.

Unlock +25% Marksman Cooldown Bonus:
Get 150 Kills using the Pistol.

ALL Exp Rewards Improved by 5%:
Reach Level 60.

Spectre Grade Weapons for Purchase:
Get 1,000,000 Credits.

Unlock Assault Rifle Skill for New Characters:
Get 150 Kills using the Assault Rifle.

Unlock Shotgun Skill for New Characters:
Get 150 Kills using the Shotgun.

Unlock Sniper Rifle Skill for New Characters:
Get 150 Kills using the Sniper Rifle.

Unlock Decryption Skill for New Characters:
Use Sabotage 75 times.

Unlock Electronics Skill for New Characters:
Use Overload 75 times.

Unlock Shielding Skill for New Characters:
Use Dampening 75 times.

Unlocks Talent 'Barrier' for Future Characters:
Use Barrier 75 times.

Unlocks Talent 'Reverse Engineering' for Future Characters:
Use Hack 75 times.