Learn Hardcore Portuguese (Portugal): O céu ficou escuro de repente, mas o festival continuou com a mesma energia. - The sky suddenly became dark, but the festival continued with the same energy.

O céu estava escuro. → The sky was dark.
This just describes a state in the past, without focusing on the moment it changed.
O céu está escuro. → The sky is dark.
This is present tense, describing how the sky is now, not what happened.

So ficou highlights that the sky turned dark at that moment, which fits well with de repente (suddenly).

What does ficar mean here? I thought it meant “to stay”.

Ficar is very flexible in Portuguese. Two of its common uses are:

“To stay/remain”
- Ficámos em casa. → We stayed at home.
“To become / to get (a certain way)” — that’s the meaning in your sentence
- O céu ficou escuro. → The sky became dark / got dark.
- Fiquei cansado. → I got tired.
- Ela ficou feliz. → She became happy / got happy.
- A comida ficou cara. → Food became expensive / got expensive.

In O céu ficou escuro, ficar + adjective = to become + adjective.

Could we say O céu escureceu de repente instead of O céu ficou escuro de repente?

Yes, you can, and it is correct:

O céu escureceu de repente.
Literally: The sky darkened suddenly.

Differences in nuance:

Ficou escuro:
- Uses ficar + adjective → became dark / got dark.
- Very common and neutral in everyday speech.
Escureceu:
- Uses the verb escurecer (to darken).
- Slightly more “verbal” and maybe a bit more literary or descriptive, but still perfectly normal in speech.

Both sound natural. In casual conversation, ficou escuro is extremely frequent; in narratives or more descriptive writing you’ll see both.

Why is there a comma before mas?

In Portuguese, you normally put a comma before coordinating conjunctions like mas (but) when they join two clauses:

O céu ficou escuro de repente, mas o festival continuou com a mesma energia.

Two full clauses:

O céu ficou escuro de repente
(Mas) o festival continuou com a mesma energia

Because each part could, in principle, stand on its own as a sentence, you separate them with a comma + mas. Leaving the comma out here would usually be seen as incorrect in standard writing.

Could we use porém, no entanto, or só que instead of mas? Are they the same?

They’re similar (all introduce contrast), but not identical in tone or position:

mas
- Most common, most neutral for “but”.
- Normally comes right before the clause:
  - … mas o festival continuou com a mesma energia.
porém / no entanto
- Closer to “however / nevertheless”.
- More formal or literary.
- Can appear after a comma, often more flexible in position:
  - O céu ficou escuro de repente; porém, o festival continuou…
  - O céu ficou escuro de repente. No entanto, o festival continuou…
só que
- Colloquial, often used in speech, similar to “it’s just that / except that”.
- E.g.: O céu ficou escuro de repente, só que o festival continuou com a mesma energia.
- Sounds more informal and conversational than mas.

In your sentence, mas is the most straightforward and neutral choice.

Why do we use ficou and continuou (simple past) instead of ficava and continuava (imperfect)?

Portuguese distinguishes two main past tenses:

Pretérito perfeito (simple past):
ficou, continuou
→ Describes completed events seen as whole units.
- O céu ficou escuro de repente: it became dark at that moment.
- O festival continuou: it continued (despite that).
Pretérito imperfeito (imperfect):
ficava, continuava
→ Describes ongoing / repeated / background actions or states.
- O céu ficava escuro sempre que chovia.
  → The sky would get dark whenever it rained. (repeated habit)
- O festival continuava enquanto chovia.
  → The festival was continuing while it rained. (background action)

In your sentence, we’re telling a concrete little story: the sky got dark, but the festival carried on. Both are events, so ficou and continuou (pretérito perfeito) are the natural choice.

Why is it escuro and not escura?

Because adjectives in Portuguese agree in gender and number with the noun they describe.

céu is a masculine singular noun: o céu
So the adjective must also be masculine singular: escuro

Examples:

O céu está escuro. (masc. sg.)
A noite está escura. (fem. sg.)
Os céus estão escuros. (masc. pl.)
As noites estão escuras. (fem. pl.)

So O céu ficou escuro is correct; O céu ficou escura would be grammatically wrong.

Can I drop the article and say Céu ficou escuro or Festival continuou?

Normally, no. In standard Portuguese, you almost always need the definite article with specific nouns:

O céu ficou escuro…
O festival continuou…

Without the article:

Céu ficou escuro… – sounds wrong in normal prose/speech.
Festival continuou… – sounds like a headline or note, not standard sentence.

Where you might see the article dropped:

Headlines / notes:
- Céu fica escuro, festival continua.
Poetry / song lyrics, where grammar can be more flexible.

In ordinary sentences, keep o: o céu, o festival.

What does de repente literally mean, and can it go in other positions?

Literally:

de = of / from
repente = from repentino (sudden)

So de repente is an idiomatic phrase meaning “suddenly / all of a sudden”.

Position:

Very common after the verb or at the end of the clause:
- O céu ficou escuro de repente. (most natural here)
It can also come at the beginning, with a comma:
- De repente, o céu ficou escuro, mas o festival continuou…

Putting it between verb and adjective (ficou de repente escuro) is possible but sounds more marked or poetic. The most natural are:

O céu ficou escuro de repente.
De repente, o céu ficou escuro.

Why is it com a mesma energia and not na mesma energia or da mesma energia?

In this context, com expresses manner or accompaniment — “with the same energy (as before)”:

O festival continuou com a mesma energia.
→ The festival continued *with the same energy.*

Alternatives:

na mesma energia – literally “in the same energy”
- This sounds odd or wrong here in European Portuguese.
- em is not normally used for this kind of “manner” expression.
da mesma energia – “of/from the same energy”
- You might use da mesma energia in a different structure, e.g.
  - Precisamos da mesma energia de ontem.
    We need the same energy as yesterday.
- But not after continuar this way.

For “continue with the same enthusiasm/vibe/energy”, the natural preposition is com.

How is this sentence pronounced in European Portuguese?

Here’s an approximate European Portuguese pronunciation (Lisbon-style), with syllable stress in bold and a rough IPA line:

O → [u]
céu → [sɛw]
ficou → [fikow]
escuro → [ɨʃkuɾu] (often the initial e is reduced to [ɨ])
de → [dɨ]
repente → [ʁɨpẽtɨ]
mas → [maʃ] (final s often pronounced like sh)
o → [u]
festival → [fɨʃtivaɫ]
continuou → [kõtinuow]
com → [kõ] (nasal vowel)
a → [ɐ]
mesma → [meʒmɐ]
energia → [ɨnɨɾʒiɐ]

Full line (approximate):
[u sɛw fiˈkow ɨʃˈkuɾu dɨ ʁɨˈpẽtɨ, maʃ u fɨʃtiˈvaɫ kõtinuˈow kõ ɐ ˈmeʒmɐ ɨnɨɾˈʒiɐ]

Don’t worry about perfect IPA; more important are:

Final s often → [maʃ]
Many unstressed e → repente, energia
Nasal vowels: com [kõ], the -ou in ficou / continuou [ow].

Can I change the word order, for example De repente, o céu ficou escuro?

Yes. Moving de repente to the beginning is very natural:

De repente, o céu ficou escuro, mas o festival continuou com a mesma energia.

Main possibilities:

O céu ficou escuro de repente… (your original)
De repente, o céu ficou escuro…

Both are common. Starting with De repente, gives a bit more dramatic emphasis to the suddenness of the change.

Less natural:

O céu de repente ficou escuro… – possible, but sounds more marked / stylistic.

Does energia here mean physical energy, like in physics?

No; here energia is figurative, referring to:

enthusiasm,
liveliness,
atmosphere / vibe of the festival.

So continuou com a mesma energia means:

The people were still just as animated,
The mood was still just as lively,
The festival didn’t lose its “vibe” because the sky turned dark.

If it were physical energy (electricity, etc.), the context and verbs would be different, e.g.:

Estamos a poupar energia. → We are saving energy.
A energia elétrica falhou. → The electrical power failed.