Frieza, Cooler, and King Cold's reactions from seeing how powerful the other fighters are.
Especially during the U16 Vegetto VS U20 Broly fight.
U18 Pan beating up U10 Bardock. She's so cute when she's beating the snot out of someone.
The look on Jeece's face when he is told he has been picked to fight his universe's version of Frieza.
Jeece: Er... I forfeit.
Toriyama (in his robot form) is being put into the fight, his reaction to fighting someone he didn't create and thus cannot control, is priceless.
One of the colored chapter start pages has U16 Bra and U18 Bra talking about how they go about their lives with U16 Bra basically summing up "training with my family is the best part of my life" and U18 Bra tells she's basically not much different than the DBGT canon Bra at the end both go "get a life, girl" on the other.
And in another bit involving these two, after U16 Pan dies, we see U16 Bra flipping out and going SSJ out of anger at U6 Bojack killing her. U18 Bra makes comments about her U16 self being so different and Vegeta flatly tells her she could be like her if she actually trained to which she both says she doesn't like her U16 self's hair style OR the idea of being like Goku and her dad "and be all muscle and no brain." which amusingly ticks off Vegeta.
More U16/U18 interaction hijinks: After having a chat with U12 Android 16 and Future Trunks (the trunks that visited from the future from canon DBZ), U18 Gohan goes to Videl and has a little chat about him with Videl, but she says they just had a chat about that... cue U16 Gohan showing up with a *cough* and U18 Gohan going Oh, Crap! and apologizing once he notices he confused U16 Videl with his, and realizes he's in the wrong crowd, but U16 Gohan just takes it in stride since U16 and U18 Videl look exactly alike, and accepts his apology.
The special chapters revealing the history of Universe 3 (where Bardock actually listened to the guy who gave him his future sight) reveal Goku and Raditz's mom... and she's hilariously awesome. My favorite of her appearances is when she receives word that Bardock deposed King Vegeta. She's standing there with one hand up to her scouter, and one hand holding a bruised baby-Goku by the tail while shouting "Bardock did WHAT?"
Hanasia: I can see my planet from here... AND MOONS!
The introduction of Gotenks (U16) and Gotenks (U18) in their fight. And then there's Bra's and Pan's reaction.
U16 Bra: That's it, I'm going to eliminate both of them right now.
Android 16's has two reasons for joining the tournament. First to use the Dragon Balls so he can become human. Second...
Android 16: There are several Son Goku here and I'd like to kill one.
Cell realizing his Cell Jr. isn't strong enough to fight Gast, the Super Namek, takes his child inside telling him he's going to make him more powerful. When the Cell Jr. asks how Cell would make him stronger, Cell kills the Cell Jr. with a Finger Poke of Doom and creates a stronger Cell Jr. Then, after the new Cell Jr. arrives for the match, he punches said opponent in the face without touching the ground, in such a way that is guaranteed to disqualify him or reveal that this is not the same Jr. used before, Cell... facepalms.
Cell's kill-and-replace move did not go unnoticed by many of the other universes' fighters, but nobody bothers to call him out on it... immediately, anyway. By the end of the second round, everybody who had been killed during the tournament is resurrected, which includes both of the Cell Jrs. Vegitto wastes no time poking fun at him, "wondering" out loud why there would be two Juniors instead of one.
Vegitto: Try not to kill them on the way out this time!
The ending of Chapter 23 (the Universe 7 special). Vegeta's and Cui's Oh, Crap! face as the Super Namekian they've been eavesdropping on, who has curbstomped Frieza, finds them and blackmails them for help to drive Frieza's spaceship. Their faces sell the whole deal.
Zen Buu's reaction to the music being played at the beginning of the second day. He demands that the band give him the instraments, saying that he could play better. Turns out he can. Those who hear it, except guys like Idiot Hero Goku consider it Awesome Music.
Also, Zen Buu telling one of the musicians to keep playing because he is the only good one from his group.
Why did Buu single out that one musician? Because he absorbed his universe's version of that guy, which is where his musical talent comes from.
Frieza recieves an epic trolling at the hands of U13's Nappa, where he berates Frieza repeatedly and then forfeits so Frieza can't lay a hand on him without being disqualified. That's funny enough, but the real CMOF comes when Frieza lands back in his own sector, when Burter asks if he's okay. Frieza responds by backhanding Burter hard enough to make his head explode.
Buu has a few funny moments immediately after trying to absorb the entire stadium, particularly doing an impression of South Kai (well enough to make East Kai let out a "nervous" laugh) and showing Fat Buu the right way to shut up Babidi.
As well as two people in the audience calmly commenting on how interactive the show is while wrapped up by Buu-goo tentacles.
Eleim uses his dimensional cutter to attack Bra, only she dodges it...and it hits Uub, who loses his arm again. The kicker? Instead of screaming in terror, the following dialogue takes place:
Uub: Oh no, come on!!
Zen Buu: Comiiing...
How does the huge, multi-page buildup to U3 Ghost Warrior Broly end? Why, by having him being casually killed in one hit by U13 Vegeta before he can transform, of course! As one person pointed out in the comments, you can almost hear his Leitmotif be interrupted by a Record Needle Scratch.
At one point, we cut to King Kai commentating on the Gast vs King Piccolo fight when all of the sudden...
The Tenth Doctor: Say, I'm trying to enjoy the tournament, could you stop commentating all the bloody time?
Gast making the most diabolical face as he tells King Piccolo... to let himself be overwhelmed by benevolence. Yep. Gast The Stoic trolling King Piccolo.
Babidi sends a group of mind-controlled spectators into Universe 18's lodgings to take Videl hostage. The others hear the commotion, Pan runs in to save Videl... only to find Videl's already beaten them all!
Goku not recognizing his own father. Made even funnier as Goku and Bardock are the example picture for Strong Family Resemblance.
Goku: If that Bardock guy wants to win, he's got to hold out until Cold gets tired...
Vetega: "That Bardock guy" is your father, may I remind you.
Goku: For real, that's him?
Vegeta: COME ON DID YOU EVEN LOOK AT HIM?
Goku (oblivious to Vegeta's look of disbelief): Now that you mention it... He does share a striking resemblance to Raditz...
Frieza and Cooler's reaction to U3 Frieza's fifth from.
Frieza: (pleasantly surprised)Ooh! I can do it too?
Chapter 46 has U18!Vegeta vs. U13!Kakarotto. Though the end result seems obvious, U13!Goku one ups by turning into an Giant Ape, then turning Super Saiyan. Of course, someone in the background points out a resemblance...
Bystander: But this is from DBG- Salagir:*Proceeds to beat up bystander* No! Asura:*Also beating up bystander* We thought of it independently!
During the Gast vs Raichi fight, there's some thing humorous about Gast putting all of his power into a punch against Broly and breaking his arm.