Mack has a bad luck spell placed on him by the Monster of the Week, so each team member gives him a good luck charm. So the Rangers arrive for round two looking all Badass complete with dramatic music... and the last is Mack, wearing Rose's cowboy hat, Will's lucky scarf, Ronny's never-ever-washed lucky socks, Dax's ratty old shirt (his grandfather had worn it while diving in shark territory. Judging by its condition, it's safe to say we know how much good it did him. Chomp!) all over his Ranger suit, and carrying Tyzonn's lucky potted plant in one hand. They don't improve his luck, he proceeds to actually use each item in combat, with it getting yanked from his suit in the process. Once all are gone, and Mack's taken back the Plot Coupon, he charges up his lance and, with it in one hand and the potted plant still in the other, applies the Finishing Move. Awesome.
This is actually derived from the Super Sentai version of the same scene... which is even better.
Adam returning in "Once a Ranger" and kicking as much ass as the other Rangers, who are all around a decade younger than him & have powers in their civilian form.
Before that was the appearance of the SPD Red Ranger with a jaunty "Hello!". It takes people a moment to realize "Holy crap! That's Bridge!"
In "Both Sides Now", Will attacks Kamdor before morphing, and rolls the morpher's wheel along Kamdor's blade to morph. (They usually run it down their arms in the morphing Stock Footage, but you can actually roll it across anything and it'll work just as well. Just about all of the other Overdrive Rangers used this feature to awesome effect... after Will did it that time.)
In "Once a Ranger", Mack destroys the fully-grown Vulturus. While he's not the first Ranger to take out a giant-sized monster without a Megazord, he did this while unmorphed (and not even having access to his powers) and while the returning Rangers were getting their asses handed to them in the DriveMax and Flashpoint Megazords.
Tyzonn killing two of the three Fearcats by himself. Special mention goes to him killing Krazar, who was said to be more powerful than the other two.
For only being a minor/Assist Character, Sentinel Knight is really awesome looking. Not cheesy at all! His powers and abilities are pretty sweet too.
The fact that he fought and defeated Rita and Zed's son in the past doesn't hurt.
Kamdor DIES Mid Sentence. The last battle between him and Will ends with them striking each other in passing and we wait to see who will fall, something that happens often enough in PR. Only it's Will who falls. Kamdor triumphantly sheathes his swords and goes to get the MacGuffin... and falls dead in the middle of talking about it. Will drags himself to his feet afterward, and even he must admit that Kamdor was a hell of an opponent.
Mack throwing down with Moltor in the second-to-last episode, while standing inside an erupting volcano. When Power Rangers gets epic, it gets EPIC.
After losing their powers in Once a Ranger, the Overdrive Rangers all quit & return to their normal lives... Except for Mack, who still intends to help, even if all he can do is sweep the floors.