Aunt Sylvia (who died and left Monica the dollhouse) was mentioned twice before in the series. Monica argued with her by phone about the non-vegetarian lasagnas in The One with the Dozen Lasagnas (1995), with Monica responding to what apparently was Aunt Sylvia swearing at her. The second mention of her was in The One Where Old Yeller Dies (1996), when Chandler was growing a mustache (to emulate Richard), and Monica suggested that the mustache made Chandler look like Aunt Sylvia.
The giant ceramic dog that Phoebe brings to use in Monica's dollhouse had decorated the shelf by the kitchen counter in Joey and Chandler's apartment during seasons 1 and 2.
First appearance of Rachel's boss, Joanna.
The magna doodle is a cartoon that looks like Joey's face when he comes in with the chick and the duck.