Vector in particular, revealing that unbeknownst to Charmy or Espio he knew the Eggman they were fighting had been a fake all along and then revealing the real one. Even Eggman seemed shocked that he figured it out.
Vector: It's all part of being a good detective.
Also, Charmy stinging the crap out of Eggman for ripping the team off.
How about each Team's speech after Eggman gloats about his battleship at the start of the Egg Fleet level? Heck, this troper even found the Team Rose speech that Amy gives there when she calls Eggman a bloated buffoon to be epic, simply because they're mostly close to the weakest characters in the game and basically were fighting an entire armada of battleships with a hammer, Chao in a bowtie, and a fishing rod as their weapons. And this troper recently started joining in after each Team's speech by saying "Let's kick some ass!" after each Team is done with their speech and the Egg Fleet level begins.
Believe it or not, Big the Cat gets one in the form of defending Amy and Cream during their run-in with Team Chaotix when he tells them "It's not nice to tease my friends!" and does sort of get a defensive look on his face in the CGI cutscene.
Sort of, nothing. He's hissing at Vector. When a cat that huge starts making that noise and folding its ears back, it's a clear sign that you are in danger. Big just got Badass.
Big in general in this game. While most of his story in Sonic Adventure is him bumbling around through the stories of other characters simply to find and fish for Froggy with his powers amounting basically to being able to jump high, powerlift and being clever with his trusty fishing rod, Big's involvement in Sonic Heroes shows what happens when he takes those raw skills and applies them to combat and true Sonic style adventuring.
The very end of Sonic Heroes, when fighting Metal Sonic transformed. After playing through a game where the majority of enemies are pathetically cutesy, the pre-final-boss cutscene is of Metal Sonic dismantling a ginormous ship to transform into a beast of a robot, and all in a dark, seizure-inducing way too! And that's just the cutscene: as he fully transforms, you have to fight him using Super Team Sonic, where his main attacks are firing giant lasers at you, launching 50-or-so bigger-than-you rockets at you, and throwing a large air ship from the Egg Fleet at you too.
And let's not forget a 20 second long Chaos Control. By which point, you're pretty much dead unless you've been doing pretty good so far in the battle.
Not only that, it took an astounding twelve characters to take him down. That's more than it took to bring down Perfect Chaos, a godlike guardian, and Solaris, an interdimensional Cosmic Horror. Seems that determination he gets from Sonic is amplified just as much as his speed.
And keep in mind that it took 9 of those characters just to weaken him enough for the last three to finish it.
Subtle one, but Cream is willing to take on giant robot birds, multiple enemy robots, a giant robot emperor, heck, even Team Sonic and Team Chaotix just to get Chocola back. And you have to remember, she is only six years old!
Egg Fleet. The sense of just flying through the air, while Eggman's ships unload several shells at you, dodging the whole way. The best part: Sonic, with nothing but his Rocket Accel, destroys entire battleships! And he gets to do it three times.
While most would consider it That One Level, Rail Canyon is really where Sonic Heroes begins to push the HSQ into the red. Starting off as a simplistic crash course in rail grinding with a few switch puzzles, Rail Canyon quickly introduces things such as Rhino Trains, exploding rails, and entire networks of rails to grind. Pretty soon you'll find yourself free-fall-grinding through wildly flipping light rails, racing Rhino Trains down wildly waving rail sections and going through triple-rail loop-de-loops at breakneck speed before finally reaching the climax of the stage with your team grinding down the center of a giant corkscrew of rails with two GIGANTIC trains flying down the corkscrews just ahead of you in order to block your path, with the rail system after that dumping you off into another giant network that drops you off at the goal. Final Rush, the final stage of the previous game and (in)famous for being composed of 95% railways, doesn't even begin to match the sheer awesomeness that Rail Canyon brings to the party!