Continue the Adventure :
This requires you to complete the Multiplayer introduction. You're required to do this before you engage in the multiplayer portion of the game, accessed via the Main Menu.
Continue the Adventure
Complete the Uncharted Multiplayer Introduction
Get in the Game :
This requires you to complete 5 Multiplayer matches. These matches can be any type: Team Deathmatch, Plunder, or Command and you aren't required to be on the winning team.
Get in the Game
Complete 5 matches in Multiplayer
Trials by Fire :
This requires you to complete all the Trials on Moderate difficulty or higher. Access the Trials from the Multiplayer menu and complete all 15 to gain this, as well as get a better understanding of the Multiplayer game.
Trials by Fire
Complete all trials on Moderate (difficulty) in Multiplayer
Friends Forever! :
This requires you to spawn 10 Sidekicks in Multiplayer matches by earning money and then purchasing them from your inventory.
Spawn 10 Sidekicks in Multiplayer
This requires you to revive 10 allies in Multiplayer matches by holding Triangle near a downed ally - when they are knocked to the ground, but not dead yet.
Revive 10 Allies in Multiplayer