El merchandising oficial muestra la onomatopeya.

Because merchandising is treated as a masculine noun in Spanish, so it takes el.

This is common with many borrowed English words in Spanish: they get assigned a grammatical gender, and for merchandising, the usual form is masculine.

So:

• el merchandising oficial
• not la merchandising oficial

In Spain, people also sometimes use alternatives depending on context, such as los productos oficiales, el material promocional, or la mercadotecnia in more formal or regional usage, but merchandising is very common.

In Spanish, merchandising usually refers to official branded products or promotional merchandise, especially things like:

• T-shirts
• mugs
• posters
• keychains
• figures

So in this sentence, el merchandising oficial most likely means the official merchandise.

Be careful: in some business contexts, merchandising can also refer to marketing or product-presentation techniques, but here the article el plus oficial strongly suggests official merch.

In Spanish, adjectives usually come after the noun.

So:

• el merchandising oficial = the official merchandise
• la onomatopeya correcta = the correct onomatopoeia

This is the normal word order in Spanish.
Putting the adjective before the noun is sometimes possible, but it often changes the tone or sounds less natural. In this sentence, merchandising oficial is the standard order.

Muestra is the third-person singular present tense of the verb mostrar.

So:

• yo muestro = I show
• tú muestras = you show
• él / ella / usted muestra = he / she / you show(s)

In this sentence:

• El merchandising oficial = the subject
• muestra = shows
• la onomatopeya = the object

So the structure is:

• [subject] + [verb] + [object]
• El merchandising oficial muestra la onomatopeya.

Both mostrar and enseñar can sometimes mean to show, but they are not always used in exactly the same way.

• mostrar = to show, to display
• enseñar = to show, but also very commonly to teach

In this sentence, muestra sounds natural because the idea is that the merchandise displays or shows the onomatopoeia, perhaps printed on it.

So:

• muestra la onomatopeya = shows/displays the onomatopoeia

Using enseña here would be less neutral and could sound a bit less precise, depending on context.

Spanish normally uses a definite article much more often than English does.

Here, la onomatopeya means the onomatopoeia. It is feminine singular because onomatopeya is a feminine noun.

So:

• la onomatopeya
• not el onomatopeya

The article is needed because the noun is presented as a specific thing that is being shown.

Yes. Onomatopeya is the standard Spanish word for onomatopoeia.

It is a feminine noun:

• una onomatopeya
• la onomatopeya
• las onomatopeyas

It refers to a word or sound-imitating expression like:

• tic-tac
• miau
• pum
• zas

Because that would change the meaning completely.

In the original sentence:

• El merchandising oficial = the thing doing the action
• muestra = shows
• la onomatopeya = the thing being shown

So the merchandise shows the onomatopoeia.

If you say:

• La onomatopeya muestra el merchandising oficial

then the onomatopoeia becomes the subject, so it would mean the onomatopoeia shows the official merchandise, which is a different idea and probably not what is meant.

Spanish word order can be flexible, but the subject and object still matter.

A careful Spain pronunciation would be roughly:

el mer-chan-DI-sing o-fi-THYAL MWES-tra la o-no-ma-to-PE-ya

A few useful notes:

• c before i in oficial is pronounced like th in most of Spain.
• muestra begins with a diphthong mue-, sounding a bit like mwes-.
• onomatopeya has the stress on PE: o-no-ma-to-PE-ya.

If you are speaking Latin American Spanish, oficial would usually sound with s instead of th.

It depends on the context.

El merchandising oficial is understandable and very common in modern Spanish, especially in fandom, entertainment, gaming, comics, sports, and pop culture contexts.

But depending on what you want to emphasize, a native speaker might also say:

• Los productos oficiales
• El material oficial
• Los artículos oficiales
• La mercancía oficial

These can sometimes sound more purely Spanish than merchandising, but merchandising oficial is absolutely possible and widely used.

Yes. Mostrar is a stem-changing verb in the present tense: o -> ue in most forms.

Examples:

• yo muestro
• tú muestras
• él muestra
• nosotros mostramos
• vosotros mostráis
• ellos muestran

That is why the sentence uses muestra, not mostra.

This is a useful pattern to remember, because many common Spanish verbs do the same kind of change.