Ez speciális szabály.

In Hungarian, the verb to be is often left out in the present tense, third person when the sentence links a subject to a noun or adjective.

So:

• Ez speciális szabály. = This is a special rule.

This is normal Hungarian grammar, not an omission or a mistake.

You would see an expressed form of to be in other situations, for example:

• Ez speciális szabály volt. = This was a special rule.
• Én fáradt vagyok. = I am tired.
• Te fáradt vagy. = You are tired.

So in your sentence, leaving out is is exactly what Hungarian normally does.

Because Hungarian often leaves out the indefinite article egy in this kind of predicate sentence.

So both of these can be possible:

• Ez speciális szabály.
• Ez egy speciális szabály.

The version without egy can sound a bit more compact or classificatory, while with egy can sound a bit more explicit or neutral in some contexts.

For a learner, the important point is:

• Hungarian does not always need an indefinite article where English uses a/an.

So even though English says This is a special rule, Hungarian can naturally say Ez speciális szabály.

Ez means this.

In this sentence, it stands by itself as a pronoun:

• Ez = this
• speciális szabály = special rule

So ez is the subject of the sentence.

A useful comparison:

• Ez speciális szabály. = This is a special rule.
• Ez a szabály. = This is the rule / This rule

In Ez a szabály, ez is directly attached to a noun phrase with the article a.
In Ez speciális szabály, ez stands alone and the rest is the predicate.

Because in Hungarian, adjectives normally come before the noun they describe, just like in English.

So:

• speciális szabály = special rule
• jó könyv = good book
• nagy ház = big house

That word order is the normal, basic one.

No, not here.

Hungarian adjectives do not change for gender, because Hungarian has no grammatical gender like he/she or masculine/feminine noun classes.

In a basic noun phrase like this:

• speciális szabály

the adjective stays in its basic form.

That is much simpler than in many European languages. You do not have to make the adjective agree in gender or usually in number the way you might in languages like French, German, or Spanish.

They are in the basic dictionary form, which is the nominative.

• ez = this
• speciális = special
• szabály = rule

There are no case endings here because the sentence is simply identifying something.

If the noun had another role, it could take a case ending, for example:

• szabályt = rule as a direct object
• szabályban = in a rule
• szabályról = about a rule

But in Ez speciális szabály, szabály is just the predicate noun in its basic form.

A helpful rough pronunciation is:

• spe-ci-á-lis

More specifically:

• the stress is on the first syllable: SPE...
• c is pronounced like ts
• á is a long vowel
• final s is pronounced like English sh

So speciális sounds roughly like:

• SPE-tsi-aa-lish

Not perfect English spelling, but close enough to guide you.

A rough guide is:

• SA-baay

More carefully:

• sz is pronounced like English s
• a is a short Hungarian a
• bá has a long á
• ly in modern Hungarian is pronounced like j/y

So szabály sounds roughly like:

• sa-BAAY

with stress on the first syllable, because Hungarian words are normally stressed on the first syllable.

Because Hungarian spelling keeps some historical distinctions that are no longer pronounced differently in standard modern Hungarian.

Today, ly is usually pronounced the same as j.

So in pronunciation:

• ly = j = an English y-like sound

But the spelling must still be learned word by word.
So szabály is simply the correct standard spelling, even though the ending sounds like -áj.

Hungarian word order is flexible, but the basic neutral order here is:

• Ez speciális szabály.

That is the most straightforward way to say it.

If you change the order, you may create emphasis, contrast, or a more marked style. For example, moving words around can shift what is being highlighted.

For a beginner, the best takeaway is:

• use Ez speciális szabály as the normal pattern
• do not assume Hungarian word order works exactly like English word order, even when the neutral version looks similar

It is basically neutral.

None of the words are especially formal or slangy:

• ez = ordinary everyday word
• speciális = standard adjective
• szabály = standard noun

So the sentence works in normal speech and writing.

If you said Ez egy speciális szabály, that would also be neutral. The difference is grammatical style, not formality.