La profesora dice que un personaje puede cambiar mucho cuando el héroe deja de tener miedo al villano.

Because la profesora means the teacher and refers to a specific teacher.

In Spanish, singular countable nouns usually need an article or another determiner. So:

• La profesora dice... = The teacher says...
• Una profesora dice... = A teacher says...

Saying just profesora dice would normally sound incomplete.

Because decir que is introducing a statement that the speaker presents as information, not doubt or unreality.

So Spanish uses the indicative:

• La profesora dice que un personaje puede cambiar mucho...

This is like saying:

• The teacher says that a character can change a lot...

You would expect the subjunctive after expressions of doubt, denial, emotion, influence, etc., but not after a straightforward dice que.

Compare:

• Dice que puede cambiar. = She says he/it can change.
• Duda que pueda cambiar. = She doubts he/it can change.

This is about how specific each noun is.

• un personaje = a character; this is general, not identified yet
• el héroe = the hero; now we are talking about a specific role in the story
• al villano = the villain; also a specific role

So the sentence moves from a general idea to more specific story roles:

• A character can change a lot when the hero stops being afraid of the villain.

It means can change a lot or may change greatly.

Breakdown:

• puede = can / is able to / may
• cambiar = to change
• mucho = a lot

Here mucho is working as an adverb, modifying cambiar, so it means a lot, not much in the adjective sense.

Because here mucho is an adverb, not an adjective.

It modifies the verb cambiar:

• cambiar mucho = to change a lot

Adverbs do not agree in gender or number, so it stays mucho.

Compare:

• mucho cambio = a lot of change or much change → adjective/determiner-like use
• cambia mucho = he/she/it changes a lot → adverb use

Literally, it means stops having fear.

The structure is:

• dejar de + infinitive = to stop doing something
• tener miedo = to be afraid / to have fear

So:

• deja de tener miedo = stops being afraid

This is a very common Spanish structure:

• deja de hablar = stop talking
• deja de correr = stop running
• deja de llorar = stop crying

Because a + el contracts to al in Spanish.

So:

• a + el = al

That is why you get:

• tener miedo al villano

not

• tener miedo a el villano

This contraction is mandatory except when el is part of a proper name, such as a El Escorial.

Because tener miedo is commonly followed by a preposition to show what or whom someone fears.

In this sentence:

• tener miedo al villano = to be afraid of the villain

With people or specific things, a is very natural here. You may also see miedo de in other contexts, but miedo al villano is perfectly normal Spanish.

So the important pattern to learn is:

• tener miedo a alguien/algo
• tener miedo de algo can also occur in many contexts

Because this sentence is expressing a general idea, not a single specific future event.

Here cuando means something like whenever / when, in a general sense:

• A character can change a lot when the hero stops being afraid of the villain.

Spanish often uses the indicative after cuando for general or habitual situations:

• Cuando estudio, aprendo mucho. = When I study, I learn a lot.

If the sentence were about a specific future moment, Spanish would often use the subjunctive:

• Cambiará mucho cuando el héroe deje de tener miedo al villano.
• He/She will change a lot when the hero stops being afraid of the villain.

So in your sentence, deja fits the general statement.

Because its subject is el héroe, which is singular.

Breakdown:

• el héroe = singular subject
• deja = he/she/it stops

So:

• cuando el héroe deja de tener miedo... = when the hero stops being afraid...

If the subject were plural, the verb would change:

• cuando los héroes dejan de tener miedo...

Because Spanish often leaves subject pronouns out when the verb ending already shows who the subject is.

So instead of saying:

• cuando él deja de tener miedo...

Spanish naturally says:

• cuando el héroe deja de tener miedo...

And once the subject is clear, Spanish often omits the pronoun entirely:

• Deja de tener miedo. = He/She stops being afraid.

This is normal because Spanish is a pro-drop language.

Here que means that and introduces a subordinate clause.

• La profesora dice que... = The teacher says that...

Everything after que is the content of what the teacher says:

• un personaje puede cambiar mucho cuando el héroe deja de tener miedo al villano

In English, that is often optional:

• The teacher says a character can change a lot...

In Spanish, que is normally required here.

Yes, the sentence uses a very standard and neutral word order:

• La profesora = subject
• dice = verb
• que... = content clause

Inside the clause:

• un personaje = subject
• puede cambiar = verb phrase
• mucho = adverb
• cuando... = time clause

Spanish does allow some flexibility, but this version sounds natural and clear. For example, you could move mucho or the cuando clause in some contexts, but the original is the most neutral way to say it.

Because héroe is stressed on the first syllable: HÉ-ro-e.

The accent mark shows the correct stress and helps reflect the vowel pattern. This word has three syllables in standard pronunciation:

• hé-ro-e

So the written accent is necessary.

Yes. Personaje usually means character in a story, play, film, book, etc. It does not have to be a real person.

So in this sentence:

• un personaje puede cambiar mucho...

means a fictional character can change a lot. It is a very common word when talking about literature, film, or storytelling.