I was writing something out and someone said that 'You can win special armor!' as a line is incorrect. They stated that it should have an article, aka 'You can win a special armor!'

To me, both in this case are correct. I know you can't 'win special weapon', and the article would be removed only when it's a plural in this case, aka 'win a special weapon'/'win special weapons'.

If the above 'win special armor' is correct, why is that? Is there a rule or logic to why that works in this case and sounds correct?

https://www.oxfordlearnersdictionaries.com/us/definition/american_english/armor

Notice that armor is an uncountable or non-count noun. It's like scissors, flour, bread, tea, milk, and other nouns that do not have countable elements. Therefore none of the adjectives or articles that indicate a number are to be used with this noun.

Now … if the phrase had been "a suit of armor" …

(These are "count" nouns: cup, dish, child, house, tractor …
You can actually count them!)