Speed defeating Cumulus and his copy of the Mach 5, which had a nuclear bomb attached to it as he threatened to blow up the city. Because the nuke slowed the Mach 5 clone down, Speed was able to catch up, where he commanded Trixie to take the wheel as he jumped into the Mach 5 clone and fight Cumulus, which resulted in Speed throwing him out of the car before he had a chance to detonate the nuke.
Spritle and Chim-Chim averting a full-scale nuclear war by destroying the console controlling the missiles, said war would've resulted in all nations surrendering to Cumulus.
Speed's defeat of the villain in "Man Behind The Mask". He and Dr. Fantasti take down the guards in the lab where they're being forced to work with the backblast of a rocket engine. Then Speed grabs one of the guards' machine guns, and with Fantasti in tow proceeds to shoot his way to the villain's missile base so that Fantasti can use the villain's own missiles to blow the place up.
Pretty much the entire final race is one big one for Speed, especially the last lap after he restarts the car with pure determination and hot bloodedness. He then flies down the track at speeds approaching a low-flying jet fighter, moving from last to first in the course of one lap, and actually manages to throw his final opponents into the walls so they crash into each other just short of the finish line. By the end of it, his car is smoking, the paint is peeled off the sides, and the TIRES ARE MELTED FROM THE WHEELS.
It's not just Speed's driving, but how everyone reacts to it, the crowd and press go wild, Royalton has his Villainous Breakdown, and all of it capped off with the one lady reporter absolutely losing her shit and reduced to screaming in incoherent excitement.
The start of this moment is actually kickstarted by Sparky, who sees Speed start moving for exactly one second and understands, before every other racer, what Speed is about to do.
Sparky: He's gonna do it.
For the movie in general, the best scene in cinema history is possibly gangster viking car racers shooting beehives at each other.
Speed hitting his jump jacks and using Mach 5 to take out one car in mid-air, which then ricochets away to take out a second car and save Taejo's life, before Mach 5 bounces back down to the ground and continues driving, all without missing a beat. Even the two commentators are utterly aghast, with one of them asking in disbelief, "Did he really just do that?!"
Pops shows off his wrestling skills to some ninjas, then says a cool Bond One-Liner.
Trixie: Was that a ninja?
Pops: More like a non-ja. Terrible what passes for a ninja these days.
Especially because that implies he's fought ninjas before and often enough to be completely blasé about it.
The entire second act of the movie. The whole movie is fantastic, but it's the Casa Cristo race that gives us what we all wanted: Speed driving in the Mach 5 with all of the classic gadgets. This is more in line with the anime, with Speed and Racer X tearing it up across various landscapes and environments, right down to Speed wearing his anime outfit. The whole thing is solidified when, at the end, Speed cements his victory by leaping from the Mach 5 and striking that famous pose.
During the desert portion of the race, it should be noted that Taejo, X, and Speed's driving is entirely defensive. They never use any of the gadgetry on their vehicles to do anything but escape, disable other drivers' gizmos, or set them up to run into each other. The only offensive move comes from Racer X, who hops up toward one of the viking drivers to give him a knuckle sandwich. In midair. At over 200 mph.
The entire Racer family (except maybe Sparky) has one during the fight scene in the snow covered mountains. Pops flattens multiple attackers while being the only character who doesn't end up using a firearm. Because he doesn't need one.
Pops beating the stuffing out of a ninja and then kicking the guy out of a window.
The scene where Speed and X race on Thunderhead—a T-180 track—in the Mach 5 and Shooting Star, cars that are very much not T-180s, including making Dreadnought Jump. They're such Badass Drivers that they're able to drive a full lap through an infamous track not even designed for the cars they're driving!
Racer X's introduction, going one-on-one with the Mammoth Car.