Even though Treyarch received some backlash for integrating a battle royale mode instead of a traditional single-player campaign in Call of Duty: Black Ops 4, the developers out of Santa Monica have received a lot of praise since the launch of Black Ops 4. Being responsible for much of Black Ops 4's success, Blackout is being revered by both new Call of Duty fans and returning hardcore fans, and the latter can attribute much to the mode's nostalgic focus on the map and characters.
As far as nostalgia goes, Blackout does not lack in content. Blackout's map is basically a giant compilation of many fan favorite maps from previous Black Ops games, and many of its playable characters originated from earlier games in the series as well. While Shadowman can only be unlocked by purchasing Call of Duty: Black Ops 4's season pass, all other unlockable characters can be acquired by completing the character's corresponding challenge. Although these challenges vary from character to character, the formula to unlock them remains the same.
Similar to unlocking Bruno, completing Diego's challenge boils down to three basic steps: find an item, complete an action, finish the match with the item in the player's inventory. To unlock Diego, players must first find a comic book item Pulp Magazine. While finding the initial item is often the most difficult part about unlocking Blackout's zombies characters, Pulp Magazine is a little easier to find as it can be found by both killing and looting a zombie or in a supply drop. Next, players are required to kill or down an opposing player with a headshot, while still holding the item in their inventory. After that, all players have left to do is finish the match entirely with the item in their inventory; quitting the match early will not grant progress towards unlocking Diego.
It is important to note that even though players should need only one kill or down with a headshot, some Reddit users have claimed that they needed either two or three. While these claims have not been confirmed to be true or not, it is recommended to try and seize as many headshot kills or downs as possible, just to be on the safe side.
Call of Duty: Black Ops 4 is available now on PC, PS4, and Xbox One.
Source: Reddit