This is the first time it is mentioned that Darryl has a child/children, "Of course I know the jiggle, I'm a father."
When Darryl says "three witches and a baby", it's a play on the movie Three Men and a Baby
Stephine Beacham and Shannen Doherty have worked together previously on Beverly Hills 90210
In Season 1 "The Power of Two" the Book of Shadows states the ghost (Jackson Ward) could only be vanquished by a spell spoken by the spirit of one of the witches (Prue or Phoebe). In This episode Book of Shadows) states the ghost (Gilbert) could be vanquished by a potion spread over the bones of the his body or by the death of the object of the ghosts wrath (Martha). Note per this episode Jackson Ward could have been vanquished by spreading potion over his bones since Prue and Phoebe spread a potion on his crypt (which would have his bones) to summon him.
Elias is another form of the name Elijah (like the biblical prophet).