Optimus starts off the fight by ramming into Megatron (who's in bat mode), while still in vehicle mode.
Karl controlling Fortress Maximus in "Mistaken Identity".
Despite his Anti-Hero adittude, you knew anytime Ultra Magnus showed up, there was gonna be a moment of awesome.
One example, in his debut episode he's unimpressed by the Decepticons' combination form Ruination. Then promptly blasts him back into his component parts.
Another example, in the series finale ironically his refusing to take an order form Optimus. Admittedly said order involved leaving him to be killed in a futile attempt to fight Galvatron, but still awesome.
Optimus: Put me down Magnus. That's an order, got it!
Ultra Magnus: Sorry brother, no can do. Besides I work freelance, remember? I don't take orders from you.
Omega Prime being granted the mighty Matrix Blade in the series finale.
Meta: Optimus Prime lives. He makes it through the entire series without dying once. This really says something, given that this is one of about 'three' continuities of dozens where he doesn't die.