Learn Hardcore Czech: Hlavně nechci hry, kde je někdo pořád smutný a má špatnou náladu. - Above all I don't want games where someone is always sad and in a bad mood.

So it emphasizes that this is your main condition when talking about games (you especially want to avoid games with constant sadness and bad mood).

Could hlavně go in another position, like Nechci hlavně hry...? Would that change the meaning?

Word order with hlavně is flexible, but it affects emphasis:

Hlavně nechci hry, kde... – Most natural here.
Emphasis: your main concern is avoiding that type of game.
Nechci hlavně hry, kde... – Grammatically possible, but sounds less natural and a bit odd in this context.
It suggests something like: It’s not mainly games like this that I don’t want (as if there are other things you also don’t want). It shifts the focus from “this is my main condition” to “games are not the main thing I don’t want”.

In everyday speech, for your meaning, speakers strongly prefer Hlavně nechci... at the beginning.

Why is it hry and not her? What case is hry in?

The base form is hra (a game).

Hry here is accusative plural, because it’s the direct object of nechci:

(Já) nechci co? – hry.
(I) don’t want what? – games.

For hra:

Nominative singular: hra (one game)
Accusative singular: hru
Nominative plural: hry
Accusative plural: hry
Genitive plural: her

So hry is correct because you “don’t want games” (direct object).
Her would be genitive plural and would be used in other structures, e.g.:

Nemám rád hry, bez her se obejdu.
I don’t like games, I can do without games. (without games → genitive plural her)

Why isn’t it žádné hry (“any games”)? Are nechci hry and nechci žádné hry both possible?

Both are possible, but they differ slightly in nuance.

Nechci hry, kde...
Literally: I don’t want games where...
In context, it usually means I don’t want (these kinds of) games – you’re talking about a specific category of games and rejecting it.
Nechci žádné hry, kde...
Literally: I don’t want any games where...
This adds extra emphasis on any: absolutely no games of that sort.

In this sentence, nechci hry, kde... is already clear and natural; the context itself limits it to that type. Adding žádné would make the refusal stronger or more emphatic, but isn’t necessary.

What is the function of kde here? It usually means “where”, but this isn’t really about a place.

You’re right that kde literally means where, but in Czech it is also very commonly used as a kind of relative conjunction for “where / in which / in which situation”.

In hry, kde je někdo pořád smutný..., kde roughly means:

hry, kde...
≈ games where...
≈ games in which...

So kde introduces a relative clause describing the type of games:

games where someone is always sad and in a bad mood.

More formal or explicit alternatives are possible:

hry, ve kterých je někdo pořád smutný...
(literally: games, in which…)

But hry, kde... is very natural and common in everyday speech.

Why is it kde je někdo pořád smutný and not kde někdo je pořád smutný? Does that word order matter?

Both orders are grammatically possible, but they differ in naturalness and emphasis.

kde je někdo pořád smutný – neutral, standard word order.
After kde, the verb often comes early, and this flow sounds most natural here.
kde někdo je pořád smutný – possible, but marked.
This pushes někdo (someone) forward and can sound like you’re stressing who is there, as if you’re hinting that there is some person (someone specific or surprising) who is always sad.

In your neutral, descriptive sentence about a general type of game, kde je někdo pořád smutný is the typical, unmarked choice.

What exactly does někdo mean here? Is it like “someone” or “anyone”, and could you say nějaký člověk instead?

Někdo is an indefinite pronoun meaning someone / somebody.

In this sentence:

kde je někdo pořád smutný
≈ where there is someone who is always sad
(it doesn’t matter who, just some person/character)

You could say nějaký člověk (“some person”), but:

nějaký člověk sounds more concrete and slightly heavier: a certain person, some person, often used when you want to emphasize the “person” aspect more, or contrast with something else.
někdo is lighter and much more natural here for “some character / someone”.

So někdo is the best, most neutral choice.

What does pořád mean here, and how is it different from vždycky or stále?

Pořád here means all the time / constantly / always.

In kde je někdo pořád smutný:

pořád smutný ≈ sad all the time, constantly sad.

Rough comparison:

pořád – very common in speech; “all the time”, often with a slightly emotional tone (it can sound like you find it excessive or annoying, depending on context).
vždycky – “always” in a more straightforward, general sense.
stále – “still / continuously / constantly”, slightly more neutral or formal.

You could also say:

kde je někdo vždycky smutný – grammatically fine, but a bit less colloquial-feeling than pořád.
kde je někdo stále smutný – sounds more formal or literary.

In casual, spoken Czech describing a mood in games, pořád is a very natural choice.

Why is it má špatnou náladu (“has a bad mood”) instead of something with je (“is”)?

Czech usually expresses “being in a good/bad mood” with the verb mít (to have) plus nálada (mood) in the accusative:

mít dobrou náladu – to be in a good mood
mít špatnou náladu – to be in a bad mood

So:

a má špatnou náladu
literally: and (they) have a bad mood
idiomatically: and (they) are in a bad mood.

Using je directly with nálada is not natural here. You would not say:

✗ je špatná nálada to mean “he is in a bad mood”
(that would be more like “there is a bad mood (in the room)”).

For a person’s mood, Czech prefers mít + (dobrou/špatnou) náladu.

Why is it špatnou náladu (with those endings)? What are these forms?

Nálada (mood) is a feminine noun.

In má špatnou náladu:

náladu is accusative singular feminine (direct object of má).
špatnou is the accusative singular feminine form of the adjective špatný (bad), agreeing with náladu in:
- gender (feminine),
- number (singular),
- case (accusative).

So the pattern is:

nominative: špatná nálada (a bad mood)
accusative: špatnou náladu (have a bad mood)

The ending -ou on špatnou and -u on náladu show that both are accusative feminine singular.

Why is there no comma before a má špatnou náladu?

In Czech, when two verb phrases share the same subject and are joined by a (and), there is usually no comma:

kde je někdo pořád smutný a má špatnou náladu

Here, both je (is) and má (has) have the same logical subject někdo (someone). This is treated as one coordinated predicate inside the same clause, so no comma is needed.

If you added something that made the structure more complex (different subjects, extra words), you might sometimes see a comma, but in this simple coordination, the correct standard punctuation is without a comma before a.