Betcha can't stick it...

Halo 2: Stick a Plasma Grenade to a Stealth Elite on Outskirts.

Cowardly Grunt

Halo 2: Listen to the Cowardly Grunt's woes.

Siege of Ivory Tower

Halo 2: Listen to a hidden music cue in Halo 2.

THE Chips Dubbo?

Halo 2: Fight alongside the legendary Chips Dubbo and listen to his words.

Rex Sword

Halo 2: Grab the energy sword on the level Outskirts.

10 Minutes Too Early

Halo 2: In The Oracle, find the holo-drone before the Heretic Leader activates it.

HI BEN

Halo 2: Oh, hi!

Animal Habitat

Halo 2: Spot the hippo on the walls of Headlong in classic multiplayer.

Sid Graffiti

Halo 2: Spot the Sid graffiti on the walls of Coagulation in classic multiplayer.

E E E

Halo 2: View both signs in the level Metropolis.

Why So Serious

Halo 2: View the smiling face in the classic multiplayer map Coagulation.

Why Am I Here?

Halo 2: View this hidden message on the classic Beaver Creek map.

GOOOAAAAALLLL!

Halo 2: Shoot the soccer ball in the level Metropolis.

Needs More Whammy Bar

Halo 2: Complete the level Regret with the Prophet Birthday Skull activated.

Like Peanut Butter and Chocolate

Halo 2: Complete a level in co-op on Heroic or Legendary with the Masterblaster Skull active.

Starved For Shields

Halo 2: Complete a level with only the Streaking Skull active on Heroic or Legendary.

Commuter

Halo 2: Complete Metropolis without entering a vehicle on Heroic or Legendary.

He Never Gets Me Anything

Halo 2: Complete Delta Halo without entering a vehicle on Heroic or Legendary.

Scarab Lord

Halo 2: Acquire the Scarab Gun.

Silent but Deadly

Halo 2: Kill 7 opponents from behind in a row without being spotted.

Demon

Halo 2: Complete any campaign level without dying on Normal or harder.

Go Ape Shiv

Halo 2: Kill an enraged, berserk Brute using melee.

Grand Theft Halo

Halo 2A MP: In one match, steal a total of 5 occupied vehicles from opponents.

Tour of Duty

Halo 2A MP: Complete a game in every one of the 6 updated Anniversary MP maps.

Double Down

Halo 2A MP: In Anniversary multiplayer, receive 2 or more Double Kill medals.

Warden

Halo 2 MP: In Classic or Anniversary matchmaking, stop the killing spree of another player.

Blown Out of the Sky

Halo 2A MP: Blow up the Banshee or Hornet in flight while piloted, with the Rocket Launcher.

Decorated Warrior

Halo 2A MP: Get awarded at least 10 different medals in one multiplayer game.

Ninja Redux

Halo 2A MP: Kill 5 people with melee from behind in Anniversary matchmaking.

Flaming Ninja Anniversary

Halo 2A MP: Kill an opponent that has the Ninja Redux achievement in Anniversary matchmaking.

Legend Slayer

Halo 2A MP: Kill an opponent that has the Legendary Anniversary achievement.

Back At It

Halo 2: Play a game of Halo 2 Anniversary on the 9th of any month.

Back for More

Halo 2: Complete the LASO campaign playlist.

Monopolized

Halo 2: Complete all Halo 2 Legendary campaign missions in under 3 hours.

Landfall

Halo 3: Complete Sierra 117.

Holdout

Halo 3: Complete Crow's Nest.

The Road

Halo 3: Complete Tsavo Highway.

Assault

Halo 3: Complete The Storm.

Cleansing

Halo 3: Complete Floodgate.

Refuge

Halo 3: Complete The Ark.

Last Stand

Halo 3: Complete The Covenant.

The Key

Halo 3: Complete Cortana.

Return

Halo 3: Complete Halo.

Speedy One One Seven

Halo 3: Beat the par time on Sierra 117.

Time Shift

Halo 3: Beat the par time on Crow's Nest.

Highway Robbery

Halo 3: Beat the par time on Tsavo Highway.

Lightning Strike

Halo 3: Beat the par time on The Storm.

Dambuster

Halo 3: Beat the par time on Floodgate.

Waypoint

Halo 3: Beat the par time on The Ark.

Scarab Slide

Halo 3: Beat the par time on The Covenant.