Successfully complete the Exo Survival Bonus Wave.

Note: If a friend has unlocked the Riot map, which is required to earn this trophy, then they can invite you and you can play the map straight away. This is a much quicker way of getting it.

This is the most time consuming trophy that requires actual work to be done. In order to unlock the Exo Survival Bonus, you need to unlock the Tier 4 map called "Riot". To unlock Tier 4 though, you need to play a lot of survival. The unlock requirements are as follows:

Tier 1 Maps (unlock by default)

Bio Lab
Retreat
Detroit
Ascend

Tier 2 Maps (Play 50 Rounds on Tier 1 Maps)

Horizon
Comeback
Terrace
Instinct

Tier 3 Maps (Play 75 Rounds on Tier 2 maps)

Greenband
Solar
Recovery
Defender

Tier 4 Maps (Play 100 Rounds on Tier 3 maps)

Riot

Once you have actually unlocked the map, you need to complete the first 10 waves on it. Once you have done that, you'll get the bonus wave. You need to pick up a gun first as you only spawn with a pistol, and you cannot buy anything. A HBRa3 can be found just a head of where you spawn in, and an EM1 in the room next to it behind the front counter. Now all you need to do is complete the wave. It's fairly easy, zombies will come running at you (much like how zombies mode is on Black Ops) and you just need to avoid getting hit by them. A few minutes in, you will be told to escape. Simply run to the marker, and that will complete the round. The trophy will unlock during the cutscene at the end.