El mazo está a punto de acabarse.

Estar a punto de + infinitive means to be about to + verb.

So:

• está a punto de acabarse = it is about to run out / it is about to be finished

It is a very common Spanish structure for something that is imminent.

Examples:

• Estoy a punto de salir. = I’m about to leave.
• El tren está a punto de llegar. = The train is about to arrive.

It is a fixed expression, so you normally learn it as a whole: estar a punto de.

Because Spanish uses estar in the expression estar a punto de.

This is not describing a permanent characteristic of the noun; it is describing a current situation or state: the deck is on the verge of being used up.

So:

• estar a punto de = to be about to
• not ser a punto de

In other words, you should treat estar a punto de as a set phrase.

Because a punto de is the full fixed phrase.

The pattern is:

• estar a punto de + infinitive

For example:

• Está a punto de llover.
• Estamos a punto de empezar.
• El mazo está a punto de acabarse.

You cannot normally leave out the de here.

Because acabarse and acabar do not mean exactly the same thing.

In this kind of sentence, acabarse often means:

• to run out
• to be used up
• to come to an end

So El mazo está a punto de acabarse suggests that the deck is nearly used up / nearly finished.

Compare:

• acabar = to finish, to end
• acabarse = to get finished, to run out, to come to an end

Examples:

• Voy a acabar el libro. = I’m going to finish the book.
  (I finish it.)
• El papel se está acabando. = The paper is running out.
  (The paper itself is being used up.)

That reflexive/pronominal se is very common when talking about supplies, time, food, batteries, money, etc. running out.

Here, se is part of the pronominal verb acabarse.

It does not mean himself / herself / itself in the literal reflexive English sense here. Instead, it helps create the meaning to run out / to be finished up.

So:

• acabar = to finish / to end
• acabarse = to be used up / to run out / to come to an end

Common examples:

• Se acabó el café. = The coffee ran out.
• Se me acabó el tiempo. = I ran out of time.
• Las entradas se están acabando. = The tickets are running out.

This is one of those cases where the pronominal form has its own natural meaning and is best learned as vocabulary.

Because the infinitive here is acabarse, and the se belongs to that verb.

In Spanish, object/reflexive pronouns are often attached to an infinitive:

• acabarse
• irse
• levantarse

In this sentence, the structure is:

• está a punto de + infinitive

So the infinitive remains whole: acabarse.

You would not say:

• El mazo se está a punto de acabar. ❌

That sounds wrong because a punto de separates the conjugated verb from the infinitive structure, and the se stays with acabarse.

That depends on context, because mazo has several meanings in Spanish.

Common meanings include:

• deck (for example, a deck of cards)
• mallet or hammer
• bundle or stack, in some contexts

In Spain, mazo can also be colloquial in other uses, but in this sentence, if the meaning has already been given to the learner, the most likely intended sense is simply the one that fits that context.

So grammatically, El mazo está a punto de acabarse works with any context where mazo is something that can be used up or come to an end.

Yes, but the meaning changes slightly.

• El mazo está a punto de acabarse = The deck is about to run out / is on the verge of being finished.
• El mazo se está acabando = The deck is running out / is getting used up.

So:

• a punto de focuses on something imminent, just about to happen
• se está acabando focuses on the process already happening

They are close, but not identical.

Not naturally.

Even though se sometimes looks reflexive, translating it literally as it finishes itself would sound odd and usually miss the real meaning.

In this sentence, a more natural English idea is:

• to run out
• to be used up
• to come to an end

That is why learners should be careful not to force a word-for-word reflexive translation every time they see se.

No, this is not a passive sentence.

The subject is El mazo, and the verb phrase is está a punto de acabarse. The sentence is saying that the deck is near its end or is about to be used up.

A passive sentence in Spanish would look more like:

• El mazo fue acabado...
  which would be unusual here

So this is better understood as a normal sentence with a pronominal verb, not as a passive construction.

Yes, very naturally.

This pattern is common with things that can run out, end, or be used up.

Examples:

• El agua está a punto de acabarse. = The water is about to run out.
• La batería está a punto de acabarse. = The battery is about to die / run out.
• El tiempo está a punto de acabarse. = Time is about to run out.
• Las entradas están a punto de acabarse. = The tickets are about to sell out / run out.

So estar a punto de + acabarse is a very useful pattern.