All the survivors. Each of them went against all odds, using their intelligence, kindness, ruthlessness/self-preservation skills and even coming Back from the Dead (in two cases) to get back to the normal world.
Eva successfully saving both partners Lele and Oli in the death challenges they were voted into, in Episodes 2 and 9 respectively, via Eva stopping the Ungodly Machine in Episode 2 and saving Oli from the electric chair in Episode 9.
The plant monster the guests pieced together completely destroying the zombie it was up against in Episode 9, complete with the guests themselves cheering on said plant monster.
Lele shoving Matt aside after figuring out he was the one who put her into two death challenges.
The fact that Tim and Oli were spared from death in Episode 5 because the group had, earlier in the episode, returned the Guardian, Sam, to the Ringmaster's carnival.
Timothy shooting zombies and being the only one who knows how to act during a shootout.
While everyone else was running away in panic from the sniper, Timothy stayed calm and made himself small by laying on the floor.
The fact that Vincent Wells, the fourth owner of the house, was the one that planted the note warning the group about the person working with the evil of the house in the first place. Furthermore, immediately after being freed (as part of his imprisonment in the house, he was also suffering from his hallucinations while tied up in a straitjacket), points out Arthur as the one working with the evil the whole time. Vincent's last words of warning to the group before he leaves?
Vincent: If I were you, I'd run.
Arthur's brother killing Sarah, Marvin and Arthur after the guests free him in [[spoiler: Episode 10, ultimately saving the guests from an unfortunate fate at the house staff's hands.
Tana throwing the lollipop at the Sorceress in Episode 5 has been considered as her Moment of Awesome by the fandom.
Tyler's equivalent is putting on the Crown of Oblivion and thus breaking the Sorceress' spell.
Riley killing the Sorceress.
Gabbie climbing the web while wearing heels in Episode 3.
Jet Pack Girl avenging Gabbie by defeating the Promethean.
Alex defeating DeStorm in a death challenge, successfully avenging Lauren.
Mortimer and Calliope rescuing everyone from the clowns in the beginning of Episode 2.
Safiya LITERALLY DRINKING KETCHUP in order to eat five hot dogs in a row during a death challenge in Episode 2.
As for Jc, he solved the entire math puzzle without anyone's help. He secretly proves himself to be the most resourceful out of anyone by staying in the background and helping the team anyway he can.
Roi volunteering to go into the challenge because Matt saved his life earlier. Doubles as heartwarming.
MatPat doing the splits.
MatPat refusing to die a second time; in the witches' challenge, he barrels through every obstacle, being the first to complete all but the first one (in which he was second behind Joey), declaring with each one completed "I am NOT dying again!".
Calliope telling off Lucy saying they have seven of the eight artifacts and Lucy is in the way of the last one and then proceeds to threaten to "beat the crazy out of her"]] in Episode 9, which leads to [[spoiler: a really entertaining fight between the two.
Calliope: We have seven of the artifacts and YOU'RE the only one standing between us and the last one, so move your ass before I beat the crazy out of you. *pushes Lucy away*
Jael and Ryu kicking Carnival Master ass and succeed in killing him.
The last scene of the Season 3 finale featuring an original song in it! It's called No One Escapes by Catherine Keithley, and many fans agree that it was extremely fitting.
To add on to this, Tana refuses to command the Mummy to kill Justine, even though she has to do so in order to get the first Jeweled Key. Also crosses over with Heartwarming, even if it didn't work in the end.
Though also a Tear Jerker, Justine attempting to straight-up kill the Mummy before it can kill her, even though she already lost the challenge. Even if she went down, she went down fighting.
The fact that Bretman initially gathered 32 coins in the beginning of Episode 3's coin challenge, making him more than safe enough for immunity from the death challenge (whoever gathered the least amount of coins automatically went into the death challenge). This was unfortunately spoiled when Garuda caught him, making him lose half his coins, but he still managed to be safe from the challenge in the end.
From Episode 4:
Colleen acting as Miranda to make the Emperor laugh.
Gabbie's Miranda impression.
Bretman splitting a board in half in one go.
Crosses over with Heartwarming and Tear Jerker, but Destorm willingly breaking the rules and sacrificing himself for Alex in the death challenge, saying "This is for Lauren." It's a big step from where he and Alex had their previous feud in Season 2, even if the alliance they formed by Episode 3 of Season 4 was short-lived.
The next episode takes it further by having him volunteer to enter the challenge in Alex's place (whom had been through three challenges in that season alone already). As in, a challenge which he could have lost his life in, but didn't, only because of Alex's repayment and Fatima's intervention. Damn, Character Development hit him hard in two episodes alone.
Episode 7: Fatima writing Scheherazade's name onto the end of the story, dooming her, for killing her true love. You go, girl!
Episode 10: Though horrifying for the guests, The Collector brings back MANY of the minor (and some major!) villains from Seasons 1-3 as the monsters chasing the last guests, including Lucy from Season 3, the Man With No Name from Season 3, the Guardian of Season 1, the Carnival Master himself from Season 3, and even a Harpie and Vampire from Season 2!