While dressing up, Grim wears socks for the first time.
Mary Frances was credited as Unicorn #1.
Billy's Dad and Sperg weren't listed during the credits.
Mandy claims Billy's hamster Mr. Snuggles was 7 years old. In the first episode, she said it was his 10th birthday.
Irwin mentioned his brother who only had one appearance in Halls of Time was written out.
Mandy: They're right. You should sell yourself to science.
Mandy: What is ultimate power anyway?
Billy: Why mandy, everybody knows that ultimate power is (Grim joins in) dancing! (Disco appears and everybody starts dancing)
Grim: Mr. Hobnobbins, I have come for thee!
Mr. Hobnobbins: What? Me hard of hearing. Come closer so I can smell you lots better.
Grim: (louder) I said, "Mr. Hobnobbins, I have come for thee!" Now, let's go. I've got a cab waiting outside.
Mr. Hobnobbins: (laughing)
(Grim gets captured in a net)
Grim: (sarcastically) Take us somewhere cool, Grim! Somewhere that has giant sea monsters!" Well, are you happy now?!
Mandy: Um, I wanted to go to the mall. I don't remember anyone asking for giant sea monsters.
Irwin: How did we get into this mess, yo? This stuff never happens to my brother.
Mandy: Billy, I maybe a captive audience for your stupid story, but I won't let you make me look like that.
Billy: And what are you going to do about it?
(Mandy climbs down to Billy and then punches him)
Grim: I wonder if Billy is happy.
Mandy and Mary Frances: Who cares?
Grim: Good point.
Mary Frances: Grim, pass the popcorn.
Mummy: Heather, we're never going to make it to the playoffs if you keep cursing people!
Billy: It all started a l-o-o-o-o-o-n-n-n-n-n-g-g-g-g time ago in a galaxy called "Steve".
Mary Frances: (to Billy) You see? This is why I never came down here. These unicorns were all jerks; bigger jerks than me, than you! It's no wonder I stayed back. It's no wonder I hate everything. You just bring back the pain and sorrow. Why don't you just go back to where you came from and leave me alone! (kicks Billy and ran off)
Mandy: Unicorns are my kind of people.
Mandy: Billy's story is preposterous. And Grim, I don't need to be awake to tell that your version is a bunch of hooey. The way it really happened was like this. Grim came to reap Billy's 7-year-old hamster, Mr. Snuggles. We all sat and had a tea party where I challenged Grim to a duel. He took us to Limbo for a surprise; a game of limbo. Naturally, Grim underestimated my powers, and we were able to defeat him; freeing Mr. Snuggles and forcing Grim into a lifetime of friendship and servitude.
Grim: Oh, please, Mandy, that didn't even look like us!
Mandy: Raggle fraggle.
In "Billy and Mandy Begins", Mandy is hanging onto a rope, with both Irwin and Billy below, even though she is wearing a dress.
1) Mandy keeps telling Billy that he cannot force changes in others.
2) Someone keeps mentioning that something can wait.
Credits: Billy pours the cereal and it begins to talk in an evil voice. The cereal tells Billy to destroy things and Mandy, but Billy keeps saying to himself that he's imagining things. Then he pours milk in the cereal bowl and eats it.
Mandy made a flashback from the first episode of the series, Meet the Reaper.
Billy's story is probably a parody of the "Tomb Raider" game series (possibly the first as Egypt matches the Egypt Level, Greece matches the Coliseum and Amazon matches Peru).
Grim's story is probably a parody of "Star Wars".
Grim's version of their first meeting, Billy captures him with a proton pack and ghost trap just like in Ghostbusters (1984).
Billy's Story: Lord Voldemort
When Billy brings the Grim Reaper to life in his story by throwing his pieces into the cauldron, this refers to Harry Potter and the Goblet of Fire where Lord Voldemort was brought back in a similar way.
The unicorns resemble the stuffed dolls from the My Little Pony line of toys.
Grim: Surely, you jest.
Mandy: Don't call me Shirley.
This a direct reference to the movie Airplane!.
Grim's Head Retrieval: Similarity
The segment where Billy and Mandy retrieve Grim's head parodies the Steven Spielberg movie, Indiana Jones and the Raiders of the Lost Ark, namely the parts where they attempt to replace Grim's head with a bag of sand to not set off a trap and the boulder-chase sequence that follows.
Cereal Box: Bird
The cereal box on the table in the ending credits has a bird on it who resembles Toucan Sam from the Fruit Loops box.
The white thing that pops out of the cauldron during the dance number at the end of Billy's flashback is a Shmoo, originally from the L'il Abner comic strip as later used in an assortment of Hanna-Barbera Cartoons.
Mary Frances: (to Billy) Why don't just go back to where you came from and leave me alone!
This line was used from the anime movie, Akira.
Grim: (after Mandy finished telling the real story) Oh please Mandy, that didn't even look like us!
He is referring to the changes in designs from the beginning of this series.
Episode Title and Plot: The Crass Unicorn
They are references to the movie, The Last Unicorn.
Billy: It puts the lotion on its skin, or else it gets the hose again.
This is a line from the 1991 film Silence of the Lambs.
The device Billy uses to capture Grim in Grim's flashback is the same one used by the Ghostbusters movie bearing the same name.
Grim: I'll never join you!
Luke Skywalker said this exact same line to Darth Vader after their lightsaber duel in Star Wars Episode V: The Empire Strikes Back.
Equipment: Particle Beam
The equipment Billy uses to capture Grim is identical to the equipment used by the Ghostbusters.
Mandy: Raggle Fraggle.
Episode Title: Billy And Mandy Begins
This could be a reference to the latest Batman movie, Batman Begins.