Mulder's mysterious water bed comes from Dreamland II (1998) when Morris Fletcher bought himself a new water bed, thinking he would be living the rest of his life in Mulder's body, and put it in Mulder's bedroom. Mulder has no memory of those events, so he has no idea where he got his water bed from.
Darren E. Burrows (Bernard) also appeared as 'Pfieffer' in The X-Files spin off The Lone Gunmen (2001).