Learn Hardcore German: Manchmal wird mein Bruder eifersüchtig, wenn ich im Spiel gewinne, aber er lacht trotzdem. - Sometimes my brother gets jealous when I win in the game, but he laughs anyway.

wird eifersüchtig = becomes jealous / gets jealous (focus on the change of state)
ist eifersüchtig = is jealous (a state, not the process of becoming)

So:

Manchmal wird mein Bruder eifersüchtig
→ Sometimes my brother gets jealous.
Manchmal ist mein Bruder eifersüchtig
→ Sometimes my brother is jealous. (sounds more like a description of his character or mood, not tied so clearly to the event of you winning)

In this sentence, German mirrors the English idea “gets jealous when I win”, so wird is the natural choice.

Why does the sentence start with Manchmal, and what effect does that have on word order?

German main clauses follow the verb-second (V2) rule: the conjugated verb must be in second position, no matter what comes first.

Here:

Manchmal (position 1: an adverb)
wird (position 2: the conjugated verb)
mein Bruder (rest of the sentence continues)

So:

Manchmal wird mein Bruder eifersüchtig...

You could also say:

Mein Bruder wird manchmal eifersüchtig...

Both are correct. Starting with Manchmal puts a bit more emphasis on “not always, just sometimes”. The verb still stays in position 2.

Why is it mein Bruder and not meinen Bruder?

Because mein Bruder is the subject of the sentence and must be in the nominative case.

Wer wird eifersüchtig? (Who becomes jealous?) → mein Bruder (nominative)
Wen wird er eifersüchtig? (Whom does he become jealous?) → makes no sense; Bruder is not an object here.

Forms of mein with Bruder (masculine singular):

Nominative: mein Bruder
Accusative: meinen Bruder
Dative: meinem Bruder

Since Bruder is the one doing the action (becoming jealous, laughing), mein Bruder (nominative) is correct.

What exactly is im in im Spiel, and why not just in Spiel?

Im is a contraction of in dem:

in (preposition) + dem (dative article, masculine/neuter) → im

Spiel is a neuter noun: das Spiel. After in with a location/being inside, German usually uses the dative case:

in dem Spiel → im Spiel

You cannot say in Spiel; you need the article.

Im Spiel here roughly means “in the game / during the game / in the context of the game”.

Why is the word order wenn ich im Spiel gewinne and not wenn ich gewinne im Spiel?

In a subordinate clause introduced by wenn, the conjugated verb goes to the end.

Basic pattern in many subordinate clauses:
[subordinating conjunction] – [subject] – (objects/adverbs) – [verb]

So:

wenn – ich – im Spiel – gewinne

If this were a main clause, standard word order would be:

Ich gewinne im Spiel. (subject–verb–other information)

But because wenn makes it a subordinate clause, gewinne must be at the end.
Wenn ich gewinne im Spiel is wrong in standard German.

Why is wenn used here and not als or wann?

All three relate to “when” in English, but they’re used differently:

wenn
- for repeated events in the past, present, or future
  → Whenever / if / when this happens…
- fits here: Sometimes he gets jealous whenever I win.
als
- for one specific event in the past
  → When I moved to Berlin, … → Als ich nach Berlin gezogen bin, …
wann
- for questions (direct or indirect) about time
  → When are you coming? → Wann kommst du?
  → I don’t know when he is coming. → Ich weiß nicht, wann er kommt.

In your sentence, the idea is “whenever I win in the game”, a general, repeated situation → wenn is correct.

Why are there commas before wenn and before aber?

Two different rules:

Comma before wenn
- Wenn ich im Spiel gewinne is a subordinate clause.
- In German, a subordinate clause is separated by commas.
- So you need a comma before wenn (and another comma at the end of the subordinate clause if something follows).
Comma before aber
- Aber is a coordinating conjunction joining two main clauses:
  - Manchmal wird mein Bruder eifersüchtig, wenn ich im Spiel gewinne,
  - aber er lacht trotzdem.
- German normally uses a comma before aber when it links two clauses.

So both commas are mandatory in correct written German in this sentence.

What does trotzdem mean here, and where can it go in the sentence?

Trotzdem means roughly “nevertheless / nonetheless / anyway / even so”.

In the sentence:

aber er lacht trotzdem
→ but he laughs anyway / but he still laughs.

Typical positions for trotzdem in a main clause:

Trotzdem lacht er.
Er lacht trotzdem.
Er lacht trotzdem darüber. (if you add about it)

It is a sentence adverb; it usually stands near the beginning of the clause, but often after the subject:

Er lacht trotzdem. (very common and natural)
Aber trotzdem lacht er. (also fine, adds slight emphasis to trotzdem)

Why is the verb gewinne and not gewinnt or some other form?

Gewinne is the 1st person singular (ich) form of gewinnen in the present tense.

Present tense conjugation of gewinnen:

ich gewinne
du gewinnst
er / sie / es gewinnt
wir gewinnen
ihr gewinnt
sie gewinnen

In the clause wenn ich im Spiel gewinne:

Subject: ich
So the verb must be gewinne.

Could you also say Manchmal ist mein Bruder eifersüchtig, wenn ich im Spiel gewinne? What’s the difference?

Yes, it is grammatically correct, but the nuance changes slightly.

wird eifersüchtig focuses on the moment of becoming jealous, as a reaction to your winning.
ist eifersüchtig describes a state: at those times, he happens to be jealous.

So:

Manchmal wird mein Bruder eifersüchtig, wenn ich im Spiel gewinne
→ Sometimes, when I win, he gets jealous (the jealousy arises at that point).
Manchmal ist mein Bruder eifersüchtig, wenn ich im Spiel gewinne
→ Sometimes, he is jealous when I win (less emphasis on the change; more on the state that accompanies your winning).

In everyday speech, both would be understood similarly, but wird eifersüchtig matches the typical English “gets jealous” more closely.

Why do we repeat the subject er in aber er lacht trotzdem? Could we just say aber lacht trotzdem?

In standard German, you must have an explicit subject in a finite clause (except for very rare cases like commands: Komm!).

So:

aber er lacht trotzdem → correct
aber lacht trotzdem → sounds incomplete or poetic; not normal in everyday prose.

Even if the subject is the same as in the previous clause, German nearly always repeats the pronoun:

Er wird eifersüchtig, aber er lacht trotzdem.
(You don’t drop the second er the way English sometimes drops pronouns in coordination.)

What is the difference between eifersüchtig and neidisch?

Both are often translated as “jealous”, but in German:

eifersüchtig
- typically about people and relationships
- e.g. romantic jealousy, jealousy of attention
- Er ist eifersüchtig, weil ich mit anderen Freunden spiele.
neidisch
- about things / advantages / possessions
- closer to “envious” in English
- Sie ist neidisch auf mein neues Auto.

In your sentence, eifersüchtig is fine: your brother is emotionally jealous because you win, not simply envious of an object.