The Too Dumb to Live, childlike Goomba you meet in the prologue. He's too dumb to realize the terrifying situation he's in and just wants to meet a Toad for the first time. By the time you see him again, he's already turned into one of them.
His final thoughts before he finally succumbs:
Goomba: ...I never...got...to see... ...Toad...
Bowser is clearly horrifiedby his minions being forcibly turned into origami and struggles to take off the clip he's pinned to, as if he's trying to break free and save them from their horrible fate. If you look back into the hole after the Folded Soldiers leave, you can see that, despite his anger-fueled threats, Bowser looks genuinely sad about what happened to them.
Bobby's Heroic Sacrifice, not only because of how shocking it is to see a character in a Mario game actually die, especially with the Paper Mario series' reliance on Disney Death, but because of Olivia's reaction to it, specifically because he died to save her. Even Mario freaks out upon seeing Bobby light his friend's fuse, knowing just what's going to happen. When Olivia questions where Bobby went, Mario turns around, shoulders slumped over trying not to show his tears as the realization hits her. Olivia is heartbroken and loses the drive to go on, while Mario attempts to console her, fails, and is at a loss for what to do to help. Thankfully, Bobby's ghost appears before Mario and encourages him to make Olivia laugh again to help her find her resolve.
The build up to it: Olivia is trapped under a boulder by Olly. Bobby has an idea how to save her, but won't tell you what. You go on a quest to the ocean liner the Princess Peach, facing the Paper Macho that attacked the ship and caused Bobby to lose his fuse and memory to begin with (and his Bomb-rades), finding a safe on board with the item Bobby needs but still won't show it to Mario. They make it back to the boulder... what's inside? The fuse of a departed friend of Bobby's, which he uses to detonate himself at the cost of his life.
When Bobby gives his final words, he apologizes for being nervous about his time with Mario and Olivia "being a blast". He wanted to spend more time with them and is afraid to die, but still goes on with it to save his friend.
When Olivia enters the cave, you have a sequence where you talk to numerous Monty Moles who have no idea what just happened, just that a boulder got detonated. The fact that they're oblivious to Bobby's death twists it further.
One of the treasures you can find is a trophy of a giant boulder. Gee game, way to really twist the knife on that one. And the other treasure you can get in the tunnel is the Important Box that held the fuse.
After Shogun Studios is saved from Rubber Band, Mario can take cute pictures with Olivia and Bobby. If you take pictures after Bobby's death, his ghost will appear in the photos.
When meeting Bowser's Bob-omb army, Olivia confuses them for Bobby. It's a stark reminder of how much Bobby wasn't just a mere Bob-omb to her, he was a friend.
Better yet, the life of a Bob-omb in general. They essentially are the Mario equivalent to kamikaze bombers, willing to risk their lives via exploding if it gets the job done.
Kamek and Bowser Jr staying behind in Hotfoot Crater to help Mario and Bowser escape. While they turn out to be okay, the sequence follows all of the beats of a Heroic Sacrifice.
Despite the horrific things he's done, Olly gets a tragic sendoff, shortly followed by his sister. He asks Olivia to read what was written on his body, which as it turns out was a message by his creator where he expresses his hope that Olly would grow to become a fair and kind king, which Olly realizes he has utterly failed to do and ended up becoming the exact opposite. Before he unravels into a sheet of paper, he asks Olivia to use his body to create the last paper crane and set everything right. Olivia does so, and erases herself from existence in the process.
Making the above worse is the moment when Olivia meets the craftsman that created her brother and expresses hope that she can talk him out of his scheme and that origami people and paper people can live side-by-side. Instead, thanks to Olly's pride and stubbornness, it never comes to be.
The ending has Peach, Mario, Bowser, and the others lighting paper lanterns to celebrate origami and Olivia's memory, and the 100% ending has the Craftsman placing miniatures of her and her brother on the castle, finally happy together.
