Ryouga provoking Sailor Moon into attacking him, then redirecting her moon tiara to kill a youma.
Ranma and Ryouga beating Jadeite. Full stop. Especially when you remember that this is set before the two picked up their ki attacks from later in the series. They beat him entirely with their wits and fists.
And his injuries from that fight are still hampering him by the climax, which is a big reason the Wrecking Crew gets out of the whole mess in one piece.
Happosai. Incredibly perverted. Unreliable in the extreme. Hated by most of the cast for being... himself. Single handedly turns the tide against the youma army... until the generals show up, of course. Doubles as a crowning funny moment.
When the Darkmistress confronts her late in the first story, Beneda is at first panicking and thinking that there wasn't any sane hope of victory. Then she remembers the host of people she's wound up with, and that no-win situations barely slowed them down... and realizes that she's beginning to think the same as they do. She accepts her insanity with a laugh and attacks the Darkmistress without further hesitation, cementing her place as one of the Wrecking Crew.
From The Dark Lords Strike Back:
Herb and Loofah piercing through every single one of Queen Beryl's shields and shredding her lungs. This has the added effect of giving Beryl a genuine fear of Herb afterwards, as she'd needed to use the bulk of her magic to heal herself from that attack. The thought of facing him again without Metallia's backing was enough to make her shudder.
Ranma, on a Roaring Rampage of Revenge after he finds the broken corpses of all his fiances, singlehandedly turns the tide of the battle by using the Kinjakan and the Gekkaja to form a massive Hiryu Shoten Ha in the middle of the cavern, rides the storm upwards and follows it up with an even more massive Hiryu Gyoten Ha while he gathers the frankly ludicrous amounts of aura shed over the course of the battle that had pooled at the top of the cavern into a Hiryu Korin Dan so massive that it obliterates the entire battlefield and completely breaks the spirit of the pitiful few youma that survive the blast. Herb, the guy who made Beryl flee in terror and the only person present to have been on the receiving end of the last part of the combo, has an epic Oh, Crap! moment when he realizes what Ranma's planning and roars for everyone to take cover.
From The Dark Lords Ascendant:
Beneda successfully stalling Metzger, then using Hinako's Happo Fifty-Yen Satsu against some soldiers in order to keep one of their captives alive.