Nunca vi tal dano.

Because Portuguese often drops subject pronouns when the verb form already makes the subject clear.

• vi = I saw
• So Nunca vi tal dano already clearly means I never saw such damage
• You could say Eu nunca vi tal dano, but eu is usually only added for emphasis, contrast, or clarity

This is very common in European Portuguese.

Vi is the 1st person singular preterite of ver (to see).

• ver = to see
• vi = I saw

In this sentence, the preterite is used to express a completed experience. With nunca, it often corresponds to English I have never seen as well as I never saw, depending on context.

Nunca normally goes before the verb in Portuguese when it means never.

So:

• Nunca vi = I never saw / I have never seen

You do not add não here.
In Portuguese, nunca already creates the negative idea by itself in this kind of sentence.

So:

• Nunca vi = correct
• Não nunca vi = not correct

It can correspond to either in English, depending on context.

In Portuguese, Nunca vi is very often used where English would say:

• I have never seen...

So even though the verb is a simple past form, the meaning can be an experience up to now.

That is very natural in Portuguese.

Tal here means such.

So:

• tal dano = such damage

It is a determiner placed before the noun. In this sentence, it adds a sense of intensity or surprise: damage of that kind or to that extent.

It is correct and natural, but it can sound a bit formal or literary in some contexts.

It is grammatical and understandable, but it sounds somewhat formal, elevated, or literary.

In everyday speech, especially in a more informal setting, people might more often say things like:

• Nunca vi um dano assim
• Nunca vi estragos destes
• Nunca vi uma coisa destas

So tal dano is not wrong at all, but it is not the most casual everyday phrasing.

Because dano can be used as an uncountable or general noun, similar to damage in English.

So tal dano means something like:

• such damage
• damage like this
• so much damage

If you wanted to talk about several specific instances or visible types of damage, Portuguese might use a plural noun or a different word, depending on the situation.

Yes. The best choice depends on the context.

Some common alternatives are:

• estrago / estragos = damage, especially visible physical damage
• prejuízo = loss, damage in a financial or broader sense
• mal = harm, evil, wrong

For physical destruction, estrago often sounds more everyday and idiomatic than dano.

So in casual speech, someone might say:

• Nunca vi estragos destes

Yes, absolutely.

Adding eu makes the subject explicit. That can be used:

• for emphasis
• for contrast
• to make the sentence clearer in a longer conversation

Compare:

• Nunca vi tal dano = neutral, natural
• Eu nunca vi tal dano = more emphatic, like I have never seen such damage

Both are correct.

Yes, it is correct in European Portuguese.

However, in Portugal it may sound:

• a bit formal
• a bit written
• slightly dramatic or literary

A more conversational version might be:

• Nunca vi uma coisa assim
• Nunca vi tanto estrago
• Nunca vi danos assim

So the original sentence is fine, but its style is a little more elevated than everyday casual speech.

In European Portuguese, the pronunciation is more reduced than many learners expect.

A rough guide is:

• Nunca ≈ NOON-kə
• vi ≈ vee
• tal ≈ tahl
• dano ≈ DAH-noo with a reduced final vowel in European Portuguese

Very roughly as a whole:

• NOON-kə vee tahl DAH-noo

A few useful points:

• the u in nunca is clearly pronounced
• unstressed vowels are often reduced in European Portuguese
• l in tal is a clear final l, not like an English w

Yes, but the tone changes.

• Nunca vi tal dano = normal and natural
• Jamais vi tal dano = more formal, stronger, or more literary

Jamais also means never, but it is less neutral in everyday speech. It often sounds more emphatic or dramatic.

So for most ordinary situations, nunca is the safer choice.