Villains are a though one... Because not all are really too scary (for example Gaston in New Fantasyland). But one thing that should be avoided at all costs is the Magic Kingdom's MNSSHP event.
The villains are everywhere and quite outgoing in character, approach to interact much more spontaneously than on a normal Meet & Greet in the park.
As rides goes, I would stay clear of Snow White, Pinocchio and Peter Pan. Plus one adult might want to have a solo go on any other dark ride, just to check how it would work for your child. You know your 10 year old the best!
How prone to nightmares is your child with loud / busy attractions? Might want to check those too.
And if you spot a villain out and about, try to either walk around or clearly show the character or the accompanying CM that there should not be any interaction. They really do respect that!
Harry Potter and the Escape from Gringotts has Voldemort and he is pretty intense so you might want to avoid that one. Spider man has lots of villains as most superheros do
I am unsure what to suggest to you. Despicable me is a good one. No Villains at all. And Seuss Landings is pretty safe. Unless you consider Dinosaurs Villains Jurassic park section is good. Plus they have a interactive area for those who just like to explore. Diagon Alley is okay as a whole. The only area that might be iffy is knockturn alley.
A lot of the rides at US/IoA could be classified as having potentially scary "villains" or elements in them.
HP Escape from Gringott's
HP Forbidden Journey
Men in Black
Revenge of the Mummy
Transformers
Spiderman
Jurassic Park
Reign of Kong (from the Ride alongs posted on youtube)
Terminator 3d show
The Mummy. My kiddo got out of the line as fast as he could (so never rode it- line scared him enough!). The ride would really have scared him. Gringotts did too but not as bad. He did fine but didn't want to re-ride
A lot of the rides at US/IoA could be classified as having potentially scary "villains" or elements in them.
HP Escape from Gringott's
HP Forbidden Journey Men in Black
Revenge of the Mummy Transformers
Spiderman Jurassic Park
Reign of Kong (from the Ride alongs posted on youtube)
Terminator 3d show
Men in Black has rather silly looking aliens. At age 10, he may or may not be scared. Plus, he gets to shoot them himself. Empowerment!
Transformers, if he has seen the movies or cartoons, they are not as scary as some of the others mentioned.
Jurassic park depends on how he feels about raptors and T-Rex. Some kids like dinos and the "scares" from narrowly escaping them but are not creeped out.
As previously stated, you know your child the best. I would recommend spending some time on YouTube and search the ride throughs of the attractions. Some are very cartoon like, others are loud and in your face, while others are more gore, but scary to one child isn't scary to another.
My son still talks about Jurassic park lol. I thought he would need therapy. I had no idea how intense it would be...even my dd was a little nervous. As soon as the sirens starting alarming, he was like I don't think I'm going to like this. At the time I felt like a horrible parent but now we all laugh hysterically. At the end with the big T rex I thought he was going to pee his pants, but the picture we have is priceless. At the time it felt a little like child abuse.
Spiderman was intense they didn't want to ride again, we skipped the mummy and Twister...Harry Potter was fine.
One of my guys has nightmares too.
I wish we'd avoided Spiderman (3 years later he's still refusing to EVER go on it again), Men in Black he was fine with - but I knew he'd freak at the 'big monster' right at the end so I made sure he closed his eyes before we got to it. He's fine with anything dinosaur because he lived & breathed them for ages!
We haven't tried The Mummy with him, but I'm not worried about getting everything done because I know we'll go again when he's older and then at least he'll have new stuff to try!
I probably won't bother trying Kong yet either