El disfraz parece nuevo.

Because disfraz is a masculine noun in Spanish, so it takes the masculine article el.

A good rule to remember: noun gender in Spanish is grammatical, so it does not depend on whether the object is masculine or feminine in real life. You simply learn disfraz as el disfraz.

Parece comes from the verb parecer, which means to seem or to appear.

So:

• El disfraz parece nuevo = The costume seems new
• El disfraz es nuevo = The costume is new

The sentence with parece is less direct. It suggests that, based on appearance, the costume looks new, but the speaker may not know for certain.

Because the subject is el disfraz, which is singular.

Spanish verbs must agree with the subject:

• el disfraz parece = the costume seems
• los disfraces parecen = the costumes seem

Since there is only one costume here, parece is the correct form.

Nuevo is an adjective, and in Spanish adjectives usually agree with the noun they describe in gender and number.

Since disfraz is masculine singular, the adjective must also be masculine singular:

• el disfraz nuevo
• el disfraz parece nuevo

If the noun were feminine, it would change:

• la camiseta parece nueva

If it were plural:

• los disfraces parecen nuevos
• las camisetas parecen nuevas

Here nuevo is a predicate adjective. It comes after the verb parece and describes the subject el disfraz.

So the structure is:

subject + verb + adjective

• El disfraz = subject
• parece = verb
• nuevo = adjective describing the subject

This is different from el disfraz nuevo, where the adjective is placed directly next to the noun.

Yes, but that means something different in structure.

• El disfraz parece nuevo = The costume seems new
• El nuevo disfraz = The new costume

In El nuevo disfraz, nuevo is directly modifying the noun. In El disfraz parece nuevo, nuevo comes after the verb and tells you how the costume seems.

Yes, you may hear está nuevo, but it has a slightly different nuance.

• parece nuevo = it looks new / it seems new
• está nuevo = it is like new / it is in very new condition

So parece nuevo is about appearance or impression. Está nuevo is more about the actual condition.

A simple pronunciation guide is:

el dees-FRATH pa-RE-thay NWEH-boh in much of Spain

In many parts of Spain, z and soft c are pronounced like the th in thin, so disfraz sounds like dees-FRATH and parece like pa-RE-the.

In areas with seseo, or in Latin American Spanish, you may hear:

el dees-FRAS pa-RE-se NWEH-bo

The stress falls on:

• disfraz
• parece
• nuevo

Because nuevo is an adjective, not a noun.

In this sentence, nuevo is simply describing el disfraz after the verb parece. Spanish does not add an article before adjectives in this kind of structure.

So:

• El disfraz parece nuevo = correct
• El disfraz parece un nuevo = incorrect

Yes. Parecer is very flexible.

It can be followed by:

• an adjective: El disfraz parece nuevo
• a noun: Parece un disfraz caro
• an infinitive construction: Parece estar nuevo
• a clause with que: Parece que es nuevo

This makes parecer a very useful verb for giving impressions or uncertainty.

The normal and most natural order is:

El disfraz parece nuevo

Spanish does allow some flexibility for emphasis, but this is the standard order a learner should use:

subject + verb + adjective

Changing the order is usually unnecessary here unless you are trying to sound literary or give special emphasis.

The plural is:

Los disfraces parecen nuevos.

Everything changes to match the plural subject:

• el → los
• disfraz → disfraces
• parece → parecen
• nuevo → nuevos

This is a good example of how articles, nouns, verbs, and adjectives all work together in Spanish.