Obtained upon completion of the prologue.

In the beginning area, there are two explosive barrels situated against the backwall of the map. Simply walk within the vacinity of the building on the left to occasion five zombies to spawn, proceed to train them until they are all within close proximity of each other, and use the Zero-point Energy Field Manipulator (Gravity Gun)'s repulsion functionality in order to detonate them simultaneously. If struggling to amass said zombies, consider attempting to do so within the confines of the building.

Obtained upon completion of the prologue, provided that no ballistic weaponry was discharged.

The corporate logo of Aperture Science, Inc. is visible emblazoned on the side of a crane-suspended shipping container in the final area of the prologue. Simply shoot said logo with any ballistic weapon.

Obtained upon completing the prologue with Gnome Chompski in tow (there is no requirement to place him in a particular manner). Gnome Chompski debuted in Valve's 2007 title Half-Life 2: Episode Two, during which players would obtain the Gnome Alone achievement for escorting him to the end of the game. He has made subsequent appearances in various Valve titles and community-made modifications alike, including Left 4 Dead 2, Half-Life: Alyx, Amalgam, and Evacuation, with analogue achievements involving different props featuring in Estranged: Act I and Snowdrop Escape, respectively.

Obtained upon discovery of the mod's sole collectable, the Epistle 3 letter. The letter will count as collected once the player draws sufficiently close (proc may be slightly delayed).