When Arnold receives his neighbor Mr. Hyunh as a Secret Santa, he and Gerald work to give him the ultimate gift by finding his long-lost daughter.
Meanwhile, Helga struggles to find the perfect gift for Arnold.
Arnold's Christmas contains examples of:
- Big Damn Heroes: It's Helga who locates Mai, as she realizes how important the holiday is and convinces Mr. Bailey to have a change of heart and help out.
- Big Damn Reunion: Mr. Hyunh seeing Mai at the door and the two happily reunite.
- Daddy Had a Good Reason for Abandoning You: During the Fall of Saigon, Mr. Hyunh had hoped to secure passage for himself and Mai aboard a helicopter, but there was only room for one. Mr. Hyunh handed Mai to the soldier, who told him the name of the city he'd be taking her to.Mr. Hyunh: I had to make the most difficult decision of my life.
- Despair Event Horizon: Arnold crosses it briefly after he's seemingly unable to reunite Mr. Hyunh and his daughter, only for Mai to show up at the boarding house on Christmas morning thus pulling Arnold back.
- Dramatic Irony: After witnessing the Big Damn Reunion, neither Arnold nor Gerald have any idea how this happened. When Arnold questions it, Gerald says it's just a miracle and that someone is clearly looking out for him. The final scene shows Helga quietly wishing Arnold a merry Christmas.
- Earn Your Happy Ending: Arnold succeeds in reuniting Mr. Hyunh with his daughter that he spent 20 years not knowing of her whereabouts after giving her to the American soldier during the Fall of Saigon. While he may not know how it happened, Helga also succeeded in giving Arnold what he wanted for Christmas even if it meant giving up the snowboots her mother waited hours in line for.
- Flashback: When Mr. Hyunh explains to Arnold how he lived in another country, was raising a daughter, and had to give her up to save her during wartime.
- Friend-or-Idol Decision: Arnold tries to reunite Mr. Hyunh with Mai, so he makes a deal with Mr. Bailey, the head of the office of missing people, to do his Christmas shopping for him in exchange for him finding Mai. Arnold and Gerald manage to find all but one of the items on Mr. Bailey's list, a pair of Nancy Spumoni snowboots. The two look everywhere, but are unable to find them. When Helga arrives home, Miriam gives her the very same snowboots as a Christmas present, which makes her happy, as it was a genuine act of kindness from her otherwise neglectful parents (Miriam even mentions having to wait in line for eighteen hours to get them, as they must be the last pair in the city). Helga's torn between keeping the snowboots for herself or having to give them to Mr. Bailey to help Arnold find Mai, and ultimately goes with the latter.
- The Gadfly: Ernie gives Oskar coal for Christmas, both for trying to rig the Secret Santa drawing and just general obnoxious behavior. He also keeps this information to himself, as Oskar is more irritated by not knowing who did it.
- It's a Long Story: When Arnold is fishing for ideas about what to get him for Christmas, Mr. Hyunh hints that this time of year makes him remember something painful. When Arnold asks about it, Mr. Hyunh says it's complicated. Arnold says he's willing to hear it, which leads into the flashback.
- Laser-Guided Karma: At the beginning of the episode, Oskar tries and fails to rig the Secret Santa drawing so that all the other residents get him and he'll get all the presents. Once Christmas arrives, Ernie, who received Oskar in the legitimate drawing, gifts him a bag of coal as punishment for the stunt as well as all his other general jerkassery.
- Literally Laughable Question: Every time Arnold and Gerald ask a store clerk for a pair of Nancy Spumoni snowboots, the clerks laugh uproariously considering they've been sold out for months.
- Long-Lost Relative: It's revealed that, back when he was still living in Vietnam, Mr. Hyunh had a daughter named Mai—but during the Fall of Saigon (when Mai was a young toddler), he surrendered her to an American helicopter pilot to save her. By the events of this episode, Mr. Hyunh hasn't seen his daughter in at least twenty years.
- Missing Mom: In the flashbacks to when he and Mai were still living in Vietnam, we never see or hear anything about Mrs. Hyunh (Mai's mother).
- No Sense of Personal Space: When Helga's considering buying Arnold a new skateboard, Stinky oddly gets right up in her face as he cheerfully states he saw Arnold riding a board exactly like the one she's holding.
- Noodle Incident: After the flashback, Mr. Hyunh says it took him 20 years to finally get out of his old country and come to the city.
- Offscreen Moment of Awesome: In between late Christmas Eve night and Christmas morning, Helga and Mr. Bailey managed to find Mai Hyunh and direct her to her biological father.
- O.O.C. Is Serious Business: Helga is beyond overjoyed when her usually irresponsible drunk of a mom stood in line for nearly an entire day to get Helga the designer boots she wanted. The fact that one of her parents actually came through for her only makes it harder for Helga to deal with the "moral dilemma" of giving the boots away to help Arnold.
- Recycled Animation: The episode opens with footage from "Snow" of the kids playing in the snow. This results in a slight Art Shift, from the "Snow" footage animated by Hong Ying to the rest of the episode being animated by Wang Film Productions.
- Secret Santa: What the boarding house gives for the episode. Arnold's is Mr. Hyunh and he and Gerald try to find his daughter as the present. Helga's is Arnold and struggles to find the perfect gift for him until she ends up being the one finding Mr. Hyunh's daughter.
- Tragic Keepsake: Mr. Hyunh has one photo of his daughter in his apartment.
- Two Lines, No Waiting: The two major plots are Arnold and Gerald trying to find Mr. Hyunh's daughter and Helga trying to find the perfect present to give to Arnold. The two cross paths once in the toy store.
- What the Hell, Hero?: Helga delivers a subdued, pleading version of this after she gives Mr. Bailey the snow boots he wanted for his daughter. After he intends to go home anyway, Helga asks if he could honestly be that cold hearted and implores him to go back inside with her to find Mai Hyunh. Not just to reunite Mai with her father, but to make sure Arnold doesn't lose his faith in humanity.
- What You Are in the Dark: Helga wanted to find a gift for Arnold that would, "make him pine for me the way I pine for him!" When the chips are down, she never tells anyone that she was the one who convinced the city worker to keep looking for Mai. And not only that, she could've kept the boots for herself and absolutely no one besides her would've known the significance of doing so.
- You Are Better Than You Think You Are: After Arnold falls just short of closing the deal, he's left terribly depressed. Gerald tries to reassure him that he went the extra mile for a friend and demonstrated the true Christmas spirit.
- You Did the Right Thing: After hearing the story, Arnold tells a depressed Mr. Hyunh that he saved his daughter's life.
