Mój kumpel przyjdzie.

Because mój has to agree with kumpel.

• kumpel is masculine singular and is the subject of the sentence, so it is in the nominative case.
• The possessive adjective mój changes form depending on gender, number, and case.

So here:

• mój kumpel = my buddy / my friend
• both words are in masculine singular nominative

If the noun changed, mój would change too, for example:

• moja koleżanka = my female friend
• moje auto = my car
• moi koledzy = my male/mixed friends

Kumpel is informal. It means something like:

• buddy
• mate
• pal
• guy friend

It is more casual than some other words for friend/colleague.

A rough comparison:

• przyjaciel = close friend
• kolega = colleague / male friend / acquaintance
• kumpel = buddy, pal, mate

So Mój kumpel przyjdzie sounds natural in everyday speech, but not especially formal.

Przyjdzie means will come.

It is the 3rd person singular future form of the verb przyjść.

This can confuse English speakers because Polish often does not use a separate word like will. Instead, the future meaning is built into the verb form itself.

So:

• przyjdę = I will come
• przyjdziesz = you will come
• przyjdzie = he/she/it will come

Because przyjść is a perfective verb.

In Polish:

• imperfective verbs have a true present tense
• perfective verbs do not have a normal present tense; their “present” forms usually refer to the future

So:

• przychodzi = he/she is coming, comes, is in the habit of coming
  
  • from przychodzić (imperfective)
• przyjdzie = he/she will come, will arrive
  
  • from przyjść (perfective)

The perfective form focuses on the action as a complete event.

They come from different aspect pairs and mean different things.

• przyjdzie = will come / will arrive
  This is a future, one completed event.
• przychodzi = comes / is coming
  This is present or habitual, depending on context.

Examples:

• Mój kumpel przyjdzie jutro. = My buddy will come tomorrow.
• Mój kumpel przychodzi codziennie. = My buddy comes every day.
• Mój kumpel właśnie przychodzi. = My buddy is coming right now.

It is in the nominative case.

Why?

• kumpel is the subject of the sentence
• the subject is typically in the nominative

So:

• kumpel = nominative singular
• mój also appears in the nominative masculine singular to match it

This is the basic dictionary form of the noun.

Because Polish often doesn’t need subject pronouns.

In English, you must say:

• He will come

But in Polish, the verb ending often gives enough information, and if the subject is already stated, adding a pronoun is unnecessary.

Here the subject is already explicit:

• Mój kumpel przyjdzie.

So there is no need for on (he).

If you said:

• On przyjdzie.

that would mean He will come, with extra emphasis or contrast depending on context.

Yes. Polish word order is fairly flexible.

The sentence:

• Mój kumpel przyjdzie.

is a normal, neutral order.

But you could also say:

• Przyjdzie mój kumpel.

This might sound more like:

• My buddy will come
• or It’ll be my buddy who comes

The meaning stays similar, but the focus changes. Polish word order often reflects what is new, emphasized, or contrasted.

It can mean either, depending on context.

The verb przyjść often has a sense of:

• come
• arrive
• show up

So Mój kumpel przyjdzie could fit several English translations depending on the situation:

• My buddy will come.
• My buddy will arrive.
• My buddy will show up.

The prefix przy- often gives a sense of movement to a place / toward arrival.

A rough pronunciation guide:

• mój ≈ mooy
• kumpel ≈ KOOM-pel
• przyjdzie ≈ something like PSHIY-jdzhye

A few useful notes:

• ó is pronounced like u
• rz sounds like a Polish zh/sh-like sound
• dzie sounds roughly like jye in English approximation

If you want a more technical version:

• mój = /muj/
• kumpel = /ˈkum.pɛl/
• przyjdzie = /ˈpʂɨj.d͡ʑɛ/

Yes, you can, but it changes the feel a bit.

• Mój kumpel przyjdzie = my buddy will come
• Kumpel przyjdzie = a buddy / the buddy / buddy will come, depending on context

Since Polish has no articles like a or the, context does a lot of work.
Using mój makes the relationship explicit and often sounds more natural if you really mean my buddy.

Yes. Kumpel is a masculine noun, usually referring to a male friend/buddy.

A common feminine counterpart is:

• kumpela = female buddy / female friend

So:

• Mój kumpel przyjdzie. = My male buddy will come.
• Moja kumpela przyjdzie. = My female buddy will come.

Notice how mój changes to moja with the feminine noun.