Red Faction: Guerrilla contains several Easter Eggs, some of which are still undiscovered by the players. Those that are currently known have been listed here.
Old Coot is found in Mohole in the Badlands, sitting on a bench next to his shack. This old man is heavily implied to be Parker from the first Red Faction game as he reminiscences about his past and makes mention of many of the characters and situations featured in the game, but it is not known what he is doing in the Badlands or how he came to be there. He also mentions the fact that he is indestructible when the player tries to harm or kill him. In most normal play, Old Coot is invulnerable to damage- however, if the player leads him to a mission (such as the Badlands Liberation mission) and starts the mission with him close by, he becomes vulnerable, and gives a -3 to morale when killed.
A Mars Rover can be found in the Badlands. It appears at the dead end of a small gully behind several ore deposits to the southwest of the Badlands safehouse and appears as a vehicle on the minimap, although it is not drivable. It is the only indestructible prop on Tharsis.
The radio tag of "Gary Hobbes" may be linked to this rover as he says "I can't the base camp or the ROVER, and my life support's gone. Jordan, I love you."
Funny Fail Text
During "Welcome To Mars" mission, if the player kills Dan Mason, there will be a fail indicator that says "WTF? YOU KILLED YOUR BROTHER!!!"
Various Radio Tags and Shaundi from Saints Row 2
There are 36 Radio Tags spread around Tharsis on Mars, and some of them carry a nostalgic message, mostly from the previous Red Faction games. For example, a radio tag of Alias from Red Faction II can be found, containing a piece of the story. When collecting another Radio Tag in the Badlands, one at the south-east of the sector can be found belonging to Shaundi, which may relate to a character in Saints Row 2.
While standing in the upgrade building at the safehouses, the player can sometimes hear the radio operator say "Cut the chatter Freeman, we need radio silence". This is an ironic reference to the protagonist of the Half-Life series, Gordon Freeman, as Gordon is a mute in the game series and is also part of a revolution. Note, the radio operator is voiced by the person who voices Barney Calhoun in Half-Life series.