Unlock Tippmann X-7 AK-47 Paintball Marker
Select "Field Gear" (in Career mode) and enter: [Up], [Up], [Right], [Right], [Down], [Down], [Left], [Left]
Put all of your players going the same way in strategies and you will most likely win.
Easy "Predator" achievement
Go to "Multiplayer" and "Public Match". Create your own game. Set the maximum number of players to 14 and reserved slots to 13. Set the game to first 5 out of 9. Place bot players on the opposite team and be the only player on yours. Start a match on the Buffalo Field. Eliminate as many players as possible, then let the last person shoot you. When they have won four, stay put and win the last five by eliminating all the players. Rush straight to the right and the opposite team will line up on the opposite end. Keep shooting them and making new games with the same rules until you get the achievement.
Complete each achievement to get the allotted gamerscore:
Reload Skill Proficency (40) - Max out the main character's Reload Skill.
Accuracy Skill Proficency (40) - Max out the main character's Accuracy Skill.
Amateur Paintballer (150) - Finish the Career on Amateur difficulty level.
Communication Skill Proficency (50) - Max out the main character's Communication Skill.
Semi-Pro Paintballer (150) - Finish the Career on Semi-Pro difficulty level.
Speed Skill Proficency (40) - Max out the main character's Speed Skill.
Speedball Chief (50) - Win at least 50 Speedball Ranked Matches over Xbox LIVE.
Training Buff (30) - Complete all training stages.
Handling Skill Proficency (40) - Max out the main character's Marker Skill.
Predator (80) - Make at least 200 eliminations in multiplayer matches.
Pro Paintballer (200) - Finish the Career on Pro difficulty level.
Woodsball Chief (50) - Win at least 50 Woodsball Ranked Matches over Xbox LIVE.
World Tour (80) - Play a game of paintball in all the Career and Woodsball locations