3D - The title is a reference to a common phrase "Someone's 3D house of horror". The "2-D" might also be a reference to the show being in 2D.
Whenever someone puts on the 3-D glasses they see something that is really super scary to them.
"Word Play" being used throughout the episode.
Vicky's parents act like they've never met Timmy's parents before and vice versa, yet they met in Channel Chasers when Vicky's parents were first introduced. Though this may be due to Timmy wiping his parent's memories of the events that happened in the latter episode.
The temple arms on Tootie's glasses are missing in many scenes.
The Nickelodeon TV Schedule displays this episode as "Timmy's House of Horror".
Timmy could have slept in his treehouse instead of Doidle's doghouse.
When Timmy's dad says "Hold me, new friends!", the captions say YOU in place of NEW. It's as if Timmy's dad was meanly nice to Vicky's parents.
Vicky's room is colored differently than how it did in previous episodes.