Pre-ordering will unlock the Shadow Pack, which includes a special victory move to hold over your victims in multiplayer. and the soundtrack for the game. Three skins for the OWL drone are also included.
The OWL gives players additional tactical abilities while in combat. There are four unique abilities to the OWL: an area of effect stun mode that shocks enemies, a shield mode that creates frontal cover for the player, a zipline mode for reaching lower areas safely, and an attack mode for attacking any enemies in range. You can see it in action in this E3 demo video: