Learn Portuguese (Portugal): Graças a este atributo, o herói é imune ao frio. - Thanks to this attribute, the hero is immune to the cold.

The adjective imune strictly requires the preposition a to introduce the thing you are immune to. This fixed pairing is its regência nominal (adjective regime). Because frio is acting as a specific noun here ("the cold") rather than an adjective, the preposition a contracts with the masculine definite article o to create ao.

Could I use por causa de instead of graças a in this sentence?

Grammatically, yes, but graças a is a much better fit. Just like "thanks to" in English, graças a carries a positive connotation, which makes sense when talking about a useful superpower. Por causa de ("because of") is neutral and often used for negative consequences.

Is graças a also an example of regência nominal?

Yes! While the current lesson focuses on adjectives, regência nominal (nominal regime) actually covers the fixed prepositions required by nouns, adjectives, and adverbs. Here, the noun graças dictates that the preposition a must follow it, exactly like the adjective imune does.

Why use é imune (verb ser) rather than está imune (verb estar)?