Meet my Hatchet of Death (or, some other colorful description RC Lewis and I come up with at any given moment). This is how I edit myself, it is how I edit others. If you think you want to play with me and my hatchet, shoot us an email.
We all know the first line of a query is your "hook." I call the last line the "sinker." You want it to punch them in the face, in a nice, friendly kind of way that makes them unable to forget you after having read the 300 other queries in their inbox.
If you're looking for query advice, but are slightly intimidated by my claws, blade, or just my rolling googly-eyes, check out the query critique boards over at AgentQueryConnect. This is where I got my start, with advice from people smarter than me. Don't be afraid to ask for help with the most critical first step of your writing journey - the query. My comments appear in green.
SWORDS & CINDER is a fairytale retell, twisting “Cinderella” with the television show, “Supernatural.” Owen has lost everything from his past—his parents, his home, his memory. His only connection to his identity is his father’s pocket watch. Abandoned by Sir Drake, Having a name in here that you might not need again is potentially confusing, just say "abandoned by his foster father" Owen’s foster father, Lady Madelyn enslaves Owen and renames him Cinderfella. Desperate, Owen seeks solace in the woods, finding friendship and danger. Waiting in the night are monstrous creatures, hidden beneath cloaks of darkness—called shadows. His savior is a spirit warrior, named Stranger, covered in gruesome scars. Stranger’s sword dissolves the creatures into cinder. Protected by daylight, Cinderfella befriends a pretty girl, Violet, and shares his pocket watch with her. Like, he shows it to her, or they both use it to tell time occasionally? Also, if Violet is not an important character you shouldn't mention her here in the query, the same with Stranger.
Four years later, Cinderfella’s destiny collides with his present. A dying spirit warrior surrenders his sword to Cinderfella, and the castle hosts a masked ball in honor of Princess Charlotte. You make it sound like these two things are immediately related, but I'm not seeing how? When Cinderfella is forbidden to attend, like he's specifically personally not allowed to attend? Or just, he's a commoner and so he can't go? a cloaked man, identifying himself as Cinderfella’s godfather, transforms him into a prince—and his pocket watch into glass—and sends him off to win the princess. But Cinderfella is stunned to discover Princess Charlotte is his childhood friend, Violet. Heartbroken, knowing he is unworthy of the princess, I don't get why this would bum him out - quite the opposite I feel like he'd be totally thrilled. Cinderfella leaves his pocket watch for her to remember him. That pocket watch reunites the couple and leads them in the middle of a war, between spirits and shadows, knights and assassins. Unclear on who the war is between and why, and where the two fit into it. Is the castle warring against the shadows and the assassins, and therefore aren't Cinderfella and Charlotte on the same side, just fighting from different arenas?
Owen must accept he is not Cinderfella, but Owen, son of Sir Stephen of Brackenridge, and his godfather has a plan—a plan to destroy everyone Owen loves. Why would his Godfather want to destroy everyone he loves? What's to gain? If he's supposed to win the heart of the princess, and the princess is Violet, and he cares for Violet, why would the godfather want her destroyed? Confused about whether or no the godfather is good or bad. With the help of the Knights of the New Moon, their leader—Drake, and Stranger, So his stepfather is back in the mix now? Owen must use his sword to defeat the shadows, protect the princess, and destroy the greatest evil their kingdom has ever faced.
There's a lot going on here that you need to clarify. Specifically who is on what side, and who is good / bad. Also, it raises a lot of questions about his stepfather's relationship when he's abandoning him at the beginning, then returning to fight on his side at the end. This might be explained in the ms itself, but within the query this level of detail leads to confusion. Trim down the references that you don't need within the query in order to get the main point across.