Passejar la mascota és difícil.

In Catalan, the infinitive can act like a noun phrase and be the subject of a sentence.

So:

• Passejar la mascota = walking the pet / to walk the pet
• és difícil = is difficult

This is very normal in Catalan. English often prefers the -ing form, but Catalan usually uses the infinitive in this kind of sentence.

Compare:

• Fumar és dolent. = Smoking is bad.
• Llegir és important. = Reading is important.

So passejar here is not strange at all: it is the standard way to say that the action itself is difficult.

It can, but more specifically it often means to take for a walk or to stroll.

That is why it works well with la mascota.

Useful contrast:

• caminar = to walk, to move on foot yourself
• passejar = to stroll, to go for a walk, or to take someone/something for a walk

So:

• Camino cada matí. = I walk every morning.
• Passejo el gos cada matí. = I walk the dog every morning.

In this sentence, passejar la mascota means taking the pet for a walk.

Because la mascota is the direct object of passejar, and Catalan normally uses an article with nouns in cases where English may be more flexible.

Here, la mascota usually means:

• the pet, if a specific pet is meant, or
• one's pet, if the context makes that clear

So Passejar la mascota is a natural way to talk about walking the pet.

If you wanted a less specific idea, you could say:

• Passejar una mascota és difícil. = Walking a pet is difficult.

But the original sentence sounds more like a real, specific situation.

Because és is the form of the verb ser meaning is.

The accent is important because it distinguishes it from es, which is a different word used as a pronoun or reflexive marker.

For example:

• és = is
• es renta = he/she washes himself/herself

So in your sentence:

• és difícil = is difficult

The accent is not optional.

Because the subject here is the whole action passejar la mascota, and that is treated as singular.

Also, difícil has the same form for masculine and feminine singular. It only changes in the plural:

• singular: difícil
• plural: difícils

So:

• Passejar la mascota és difícil.
• Aquestes tasques són difícils.

Even though mascota is feminine, the adjective is not describing mascota directly. It is describing the whole action of walking the pet.

Yes. That is also correct and very natural.

Both word orders work:

• Passejar la mascota és difícil.
• És difícil passejar la mascota.

The difference is mostly one of emphasis and style:

• Passejar la mascota és difícil puts the activity first, making it the topic.
• És difícil passejar la mascota starts with the evaluation it is difficult..., which often sounds a bit more natural in everyday speech.

So both are good; the original sentence is perfectly grammatical.

Because in this sentence passejar la mascota is the subject or complement directly.

Catalan often says:

• És difícil estudiar. = It is difficult to study.
• És fàcil entendre-ho. = It is easy to understand it.

But difícil de + infinitive is used in a slightly different structure, usually when a noun is being described as hard to do something with:

• La mascota és difícil de passejar. = The pet is hard to walk.
• Aquest llibre és difícil de trobar. = This book is hard to find.

So compare:

• Passejar la mascota és difícil. = Walking the pet is difficult.
• La mascota és difícil de passejar. = The pet is difficult to walk.

Those do not mean exactly the same thing.

Yes. Mascota means pet in a general sense.

So it could refer to:

• a dog
• a cat
• another domestic pet

That said, in real life, passejar la mascota most naturally suggests a pet that can be taken for a walk, especially a dog.

If you want to be more specific, you can say:

• Passejar el gos = to walk the dog

That is probably even more common in everyday speech when a dog is meant.

Yes, here it is transitive.

Passejar can be used in two ways:

1. Intransitive: to go for a walk / to stroll

   • M'agrada passejar pel parc. = I like strolling in the park.

2. Transitive: to take someone or something for a walk

   • Passejo el gos cada vespre. = I walk the dog every evening.

In your sentence, it is the second use:

• passejar la mascota = to walk the pet

So if you were unsure whether Catalan allows passejar with a direct object, the answer is yes.

It is neutral standard Catalan.

Nothing in it is especially formal or slangy:

• passejar is standard
• la mascota is standard
• és difícil is standard

In everyday conversation, people might choose slightly different wording depending on context, such as:

• És difícil treure el gos.
• És difícil passejar el gos.

But the original sentence is completely normal and correct standard Catalan.