At 18:53, Trevor's head is revealed in the mirror during everyone opening presents.
In a flashback scene to the 18th century, Isaac's wife uses the word "gay" in its modern sense of "homosexual" when at the time it was synonymous with "merry". However given that it's a nightmare not a memory it wouldn't have to be historically accurate.
After Eric is revived by the possessed Sam he says that he "saw" Trevor's ghost. However, the show establishes that people who have been brought back from the dead can see still see ghosts. As Eric is in the room with Trevor's ghost he should still see him alongside the other ghosts, but he doesn't seem to.