The cause for all physchic abilities in the Warhammer 40000 universe. Also the cause for the forces of Chaos.
The warp is hard to describe, in that it is completely chaotic, yet to some a sole salvation. Psykers can communicate telepathically through it and some can use it as a sort of weapon, with physical effects. Some can rip a tear in the warp through which others may be sucked. Others can use the warp to enhance their own capabilities.
Through all these advantages though there are even more dangers. Chaotic beings and malicious daemons travel through the warp and can enter this realm through its wielder.
Psykers face a constant danger if not disciplined. The daemons can speak with these psykers and even persuade them to be possessed. The effects of possession are horrible and mutagenic, transforming the host into two beings in one body, one is constantly trying to take over all control and burst free of the conciousness of the host.
It was pure chaos, vomitted striaght out of the warp.
The warp spawn grew grotesquely from its host.
The beast had four arms, no five, i couldnt count them as they were constantly changing. The effects of the warp are terrible to behold, indeed.