Right after body-charging Zeikfried off a platform towards a black hole, Zeikfried ensnares Rudy's left arm with some kind of metal cord, and nastily gloats to Rudy about how they're Not So Different and how if he goes down, he's taking Rudy with him. Rudy's response? He blows his freakin' arm off with his BFG (cuts it off with his sword, in the original), saving himself (though incapacitating himself as well, obviously) and letting Zeikfried fall into the void. It's one of the biggest "holy SHIT!" moments in the game, mitigated slightly by the terror you feel for Rudy...which only increases when you then discover he's an Artificial Human, possibly vindicating Zeikfried's statements...
McDullen/Magdalen, Jane's Battle Butler, gets one in Alter Code F when he joins the battle by non-chalantly tossing his coat on Alhazad, the Quarter Knights' second-in-command.
Maya Schroedinger kicking Siegfried's ass so hard that the plot had to come up with a new villain for the heroes to fight.
Asgard bursting out of the innocuous statue in the first dungeon to help his masters, having gotten around the Guardian of Time sending him to the distant past by hibernating his way to the present. Now that's what you call an Implacable Man.
Lombardia destroys Siegfried once and for all with her ultimate Draconic Gun Blaster. The attack animation isn't actually any different, but it's such a coup de grace moment that you can't help but cheer in victory.
'Arnaud killing Scythe by crashing a squadron of fighter jets right on top of him.
Resident Mighty Glacier and Lady of War Raquel, challenging Hugo to a fight after seeing his ability to move while time is stopped, and proceeding to block every single one of his strikes by taking advantage of the short interval at the point of his attack when he has to continue the flow of time.
Gawnusing a pair of shotguns to shoot down all of Lambda's missiles in mid-air, breaking every law of physics along the way. While giving a Crowning Speech of Awesome. And then? He punches the one he didn't have a cartridge left for, keeping it from blowing the heroes out of the sky.
The manner in which the party begins the final battle: The door to Volsung's hall opens, and Volsung looks down the carpeted hall from upon his throne, expecting to see the party walking determinedly towards him. Instead, he sees Dean sitting in the monowheel, and Dean proceeds to rip down the hallway, ducking and weaving in between Volsung's laser defenses while shooting them down, eventually driving the monowheel up a pillar and shooting down the rest of the laser emitters in midair, landing perfectly and driving the final few meters to Volsung - only to get blasted into the air by the last laser emitter, except he doesn't let that stop him, and proceeds to grab the monowheel in midair and force it down towards Volsung (shouting a battle cry that slightly reeks of Narm) - except Volsung finally stands up and blocks the monowheel with his BFS (the S standing for spear), and the screen goes white. When it fades, we find Dean and Volsung, surrounded by flames, and after they slowly stand up, they get into a quick scuffle, moving at the speed of Dragon Ball Z, which finally ends when Dean lands on his feet, the rest of the party runs up, and the final battle begins, after Volsung proving he's a sheer badass with a slick line and the small motion of pushing up his glasses on his nose. Best. Final boss intro. Ever.
The party defeats the final boss, who promptly regenerates with an As Long as There Is Evil type speech. So they kill her again. And again. And again. They are so determined that they actually frighten the incarnation of fear itself, causing it to unravel and die for good. Awesome.