Penny gets one of these Once an Episode, foiling Dr. Claw, duping his henchmen, and saving the day (and Gadget) every time.
"The Ruby" sticks out in particular as a complete and utter owning of MAD that she pulls off without them even knowing she's there.
In "Follow That Jet", Penny manages to fly a jet plane out of the MAD base. A ten year old flying a jet plane — seriously. One of the fighter pilots she's rescuing gives her a well-deserved thumbs up.
Gadget of all people gets one in "Haunted Castle", in his few shining moments of compentency. First, when the Gadgetmobile goes over the side of the cliff with Penny and Brain inside, he is able to get them back up to safety. Later inside the castle, when Dr Claw sets the basement on fire, Gadget whips out his water-finger and puts out the fire quickly.
"Haunted Castle" is probably Gadget's best episode. He's actually investigating things and doing his job instead of wandering around nearly killing himself (though, to be fair, the leads he's following were actually obvious traps laid by Claw), helps Penny get over her fear when she's hampered by her fear of ghosts, rescues her twice, and actually realizes almost right away that it's Brain he's following, not a MAD agent; all in all spends the episode being halfway competent, making good decisions for once.
The end of that episode counts as one for Brain as well, spending the episode afraid of ghosts, then turning that fear on the episodes MAD agents, releasing his inner pit bull and chasing them around the castle dressed as a "ghost knight."
Gadget shows that even he has a Berserk Button in "The Amazon," when Dr. Claw kidnaps the scientist who gave him his gadgets. The resulting car chase is possibly the single most Bad Ass scene Gadget has in the whole show. As usual, Penny and Brain stow away in the Gadgetmobile to make sure he doesn't get hurt... and immediately wish they hadn't.
Another car chase happens during "The Invasion". Not as awesome as "The Amazon", but still pretty cool.
Claw gets one in "Dry Spell," where after Penny foils his plan to steal all the water in Metro City's reservoir and force the citizens to buy water at inflated prices, he gets pissed and decides to blow up the dam and drown the whole town. And nearly succeeds, if not for Gadget intentionally saving the day for once, which probably doubles as a moment for Gadget as well.
In "Bermuda Triangle," Claw gets so mad that Gadget is still alive that he crushes a diamond to dust with one hand in rage, which naturally cases MAD Cat and the unfortunate henchman who had to give the news to freak out at the very sight of it.
There is also an episode where Claw actually spots Penny. Normally he’s too busy growling at his goons for not killing Gadget to notice her, but it’s Creepy Awesome when he said “Get the girl.”
And then there's Photo Safari, where MAD sabotages the plane that Gadget, Penny and Brain use to fly to Africa. The plane starts to fall apart when they're high in the sky above Africa, and Gadget tries to stop them from crashing by using his copter. When that doesn't work, he uses his inflatable coat to slow their descent, uses his legs to break through the bottom of the plane and then uses his skis to substitute as pontoons/wheels so they land safely. Gadget's feet are sore after that, but otherwise he, Penny and Brain all emerge unharmed.
How about Basic Training, where Dr. Claw tries to repeatedly derail the train that Gadget, Penny and Brain are travelling on? First Dr. Claw drops a pile of rocks on the track in front of the train to make it crash, but then Gadget uses his laser to blow them up and allow the train to pass safely. Later on, Dr. Claw tries to blow up a bridge and make the train fall into a chasm, but then Gadget uses his Gadget arms and legs to bridge the gap himself, and supports the train as it runs right over him. Penny even Lampshades the fact that Gadget saved her, Brain and everything else on the train.
M.A.D. Trap; perhaps the one instance all the detective's Gadgets activate perfectly first time round, just in time to evade a huge conga of booby traps set by Claw. Oh and, once again, he gets to save Penny and Brain.
The entierety of the SNES game is pretty much Gadget's moment to shine, but the crowning moment comes at the end when Gadget goes to rescue Pennyfrom Claw's airborne hideout. Claw, having just been handed his ass by Gadget, decides to be a dick and drop Penny from the ship to plummet her doom. Gadget jumps after, catches up to her and inflates his coat, thus allowing them to float down to saftey. Doubles as a Heartwarming Moment, too.