Scrin campaign - Successfully complete the GDI and NOD campaign to unlock the four mission Scrin campaign.

GDI attack combinations - The following are attack combinations you can use in Skirmish missions:

Pitbull
Predator Tank
APC with a Grenadier Squad inside

3 or more Rifleman Squads
3 or more Missile Squads

2 APCs with Rifleman Squads inside
2 APCs with Missile Squads inside

2 Grenadier Squads
2 Rifleman Squads
2 Missile Squads

NOD attack combinations - The following are attack combinations you can use in Skirmish missions:

2 Militant Squads
2 Militant Rocket Squads

4 Raider Buggys
2 Flame Tanks
2 Scorpion Tanks

4 Raider Buggys
2 Attack Bikes

SCRIN attack combinations - The following are attack combinations you can use in Skirmish missions:

4 Buzzers
4 Disintergrators
3 Seekers (combined with Buzzers)
3 Gun Walkers (combined with Buzzers)

Achievements - Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

GDI Bronze (20 points): GDI Campaign Finished with Bronze medal and Bonus Ribbon.
Nod Bronze (20 points): Nod Campaign Finished with Bronze medal and Bonus Ribbon.
Scrin Bronze (20 points): Scrin Campaign Finished with Bronze medal and Bonus Ribbon.
GDI Silver (25 points): GDI Campaign Finished with Silver medal and Bonus Ribbon.
Nod Silver (25 points): Nod Campaign Finished with Silver medal and Bonus Ribbon.
Scrin Silver (25 points): Scrin Campaign Finished with Silver medal and Bonus Ribbon.
The McNeil Legacy (100 points): GDI Campaign Finished with Gold medal and Bonus Ribbon.
You Can't Kill the Messiah (100 points): Nod Campaign Finished with Gold medal and Bonus Ribbon.
GAME OVER! (100 points): Scrin Campaign Finished with Gold medal and Bonus Ribbon.
Something to Write Home About (220 points): Complete all of the single player campaigns.
Dr. Moebius Award (20 points): Gather 100000 tiberium in MP games.
Rookie No More (20 points): Complete Boot Camp Mission.
No life (100 points): Play MP for 100 hours.
Nod Unleashed (5 points): Completing the GDI TOW: Washington D.C.
Simon Says you LOSE (0 points): Negative Achievement: Lose a single player game 3 times in a row.
The Golding Rule (0 points): Negative Achievement: Lose 5 MP games in a row.
Mister NO it all (0 points): Negative Achievement: Skipping the Tutorial suggestion from SP.
Losing Face (0 points): Lose to someone Ranked 20 places below you in a MP Ranked Game.
GDI Campaign (80 points): Complete the GDI campaign.
Nod Campaign (80 points): Complete the Nod campaign.

Additionally, there are two secret achievements, both of which are currently unknown.