Story Progression in Act 4 - Chapter 1 (any difficulty setting)
Perform 5 headshots in a row with the BIG BONER
Story Progression in Act 3 - Chapter 4 (any difficulty setting)
Defeat Elliot Beast Boss
Story Progression in Act 3 - Chapter 3 (any difficulty setting)
Defeat 10 enemies with the Stomp Attack
Defeat Kauline Grim (Sister Grim) Boss
Story Progression in Act 3 - Chapter 2 (any difficulty setting)
Save more than 300 White Gems in your inventory
Defeat 20 enemies with the HOTBONER
Complete the Tutorial
Story Progression in Act 3 - Chapter 1 (any difficulty setting)
Defeat Maras Grim (Sister Grim) Boss
Defeat 20 enemies with the TEETHER
Story Progression in Act 2 - Chapter 4 (any difficulty setting)
Defeat George Beast Boss
Story Progression in Act 2 - Chapter 3 (any difficulty setting)
Story Progression in Act 2 - Chapter 2 (any difficulty setting)
Defeat George Human Boss
Story Progression in Act 2 - Chapter 1 (any difficulty setting)
Story Progression in Act 1 - Chapter 1 (any difficulty setting)
Start a new game for the first time. (any difficulty setting)
Survive 1 wave in a Special Ops Survival game.
Earn 1 star in Special Ops Mission Mode.
Continue playing to unlock this secret achievement.
Perform all of Sonic's moves in Act 2.
Defeat 100 enemies.
Get Rank S in an Act.
Race through the first stage.
Reach the goal without dropping any of the rings you collected in GREEN HILL Act 1.
Stop the unstoppable
Last man standing
Clear the airwaves
Solve the first riddle
Drop in on an old friend
Hammer the point home
Complete all Acts in Co-op on any difficulty.
Completed all campaign Acts on Casual or Normal Difficulty.
Killed Myrrah.