Here is the full list of all 21 Modern Combat Versus achievements.
Open 5 Multiplayer Victory Crates
Open 15 Multiplayer Victory Crates
Open 50 Multiplayer Victory Crates
Open 200 Multiplayer Victory Crates
Create or join a Clan
Reach the BRONZE LEAGUE
Reach the SILVER LEAGUE
Reach the GOLD LEAGUE
Reach the PLATINUM LEAGUE
Reach the DIAMOND LEAGUE
Reach the MASTER LEAGUE
Win 3 matches
Win 10 matches
Win 50 matches
Win 100 matches
Win 500 matches
Perform 10 kills
Perform 100 kills
Perform 500 kills
Perform 2,000 kills
Perform 5,000 kills