And here we are, with the protagonists and saviors of the finale.

You said that Sandbar wouldn´t become that relevant for the group but turns out that he plays an important role with his pony status. He manages to trick Neighsay in order to get free by pretending he is not related to them. That development from What Lies Beneath was stuck with him and he came with the help of the CMC. These 3 fillies serve to sacrifice themselves in order to leave some time for the students to resolve this threat.

They weren´t aware at all that magic was disappearing and even Smolder felt that Cozy Glow was up to something for leaving Dolores out of the way. Neighsay just unexpectedly interfered Cozy´s plans by keeping an eye over the school with the EEA principles. Not only Cozy had to get rid of Dolores, but the Chancellor and the CMC as well....just that the Student 6 showed how friendship actually was with the help of the Tree of Harmony (an entity by itself by the way) by showing the elements and aspects of how friends actually are forged.

One scary line from Cozy was: "If I don´t make friends here, I will make them somewhere else", meaning that her rook cutie mark defies the central principles of harmony, replacing them with her manipulative skills.

I also forgot to mention A Matter of Principals. This is where the two parter feels like the season 4 finale with the little objects as keys for the chest. Here they work for containing all the magic inside down below the school.

Here, the students glow (pun intended) different colors for each element (I may be implying on this part, correct me if I am wrong):
Purple- Magic for Gallus
Orange- Honesty for Yona
White- Generosity for Ocellus
Yellow- Kindness for Sandbar
Pink- Laughter for Silver Stream
Blue- Loyalty for Smolder