Sergeant Major

Corporal is one of 28 Achievementsin The Respawnables.

The description says: Reach level 20

Obviously this achievement is earned after reaching level 20. The reward for this Achievement are 15 Score Points    (when achieved during a match).

Tips & Tricks
The best way to level up is the Multiplayer Mode Free For All, since it's provides the most experience points - if being first or second place.

Another way, more pleasureable for lower levels is completing   Missions  . .