In "Grimian's Secret", the Enemy Mine with the Vandals against the Red Sentients. Epic is the only word that can describe it. The final showdown between Grimian and Kalus is also awesome.
The climax of Rumble In The Jungle. Grimian's Vandals vs. Kalus' Vandals in a massive battle. Kalus gets a major one when the Red Sentients join in. Kalus singlehandedly rallies the Vandals, stopping the Enemy Civil War to unite his planet against the Red Sentients, sparking a massive battle between them. Kalus shows just how badass he is by fighting Krytus one on one and more than holding his own. In fact, if it wasn't for the bomb the Battle Force 5 set up to destroy all Sentient tech on the planet, Kalus might actually have defeated Krytus. Even though he's no longer a major threat in the war, Kalus takes this defeat gracefully and then finally decides to execute Grimian for treason.
All of Unite And Strike!
Particular mention goes to from Tezz and AJ's Big Damn Heroes moment onwards. They rush in with the Mobi and save Vert. As the Battle Force 5's theme starts up, he's launched out of the Mobi, completing the ritual to release the Blue Sentient minds from Sage. The group's cars rise into the air, letting off a shockwave that revives all the Blue Sentients, including Sage. Sage reunites with her old friend Boralis, floating into the air and using the fusion energy from the cars to fire a beam of blue energy that blows away the Red Sentient 5. Then Krytus reforms back on the Red Sentient homeworld, only to discover that Sage beat him there and made peace with the Red Sentients. Sage then banishes Krytus for good, ending his war once and for all.