Confront Dr. Nefarious in the past.

Collect a Spybot

Defeat the Wigwump.

Buy half of the weapons.

Kill an Enemy While Playing as an Alternate Character Costume Other Than Drake

Kill 50 Enemies with the M4

Kill 50 Enemies with the 92FS - 9mm

Kill 30 Enemies with the MP40

Kill 100 Enemies with Headshots

Kill 5 Enemies in a Row with Headshots

Kill 50 Enemies with the Micro-9mm

Complete Career Mode

Complete the Fishing Boat bow, steps and main deck first