Are different Spanish adverb types normally mixed?
What I know:
Some Spanish adverbs can have up to three 'types": one, normally just the masculine form of the adjective, eg "rápido"; the second the feminine form of the adjective plus the -mente suffix, eg "rápidamente"; and the third "con + noun", eg "con cuidado" (I wasn't sure if "con rapidez" was a valid example 
).
When two -mente adverbs follow a verb the first adverb loses the -mente suffix. eg "Ella respiraba lenta y profundamente."
What I don't know:
When two adverbs follow a verb, can they be of mixed type, and if so is it commonly done?
And, if the adverbs can be of mixed type, and the first is a -mente form, does it still lose that suffix?
Below are some examples for the above. I've arranged them in what I'm guessing is best to worst order but would appreciate corrections/comments.
Ella habla lenta y claramente
Ella habla lento y claro
Ella habla lento y con claridad
Ella habla lenta y con claridad
Ella habla lenta y claro
Ella habla lento y claramente
Ella habla lentamente y con claridad
Ella habla lentamente y claro
2 Answers
I researched my textbooks for information on this and couldn't find any rules. All I can go by is what sounds right to me after speaking Spanish all my life.
I like your sentences 1,2,3. #'s 4,5,6 do not sound correct. #7 sounds OK but 8 doesn't.
Maybe someone who knows their way around the RAE can give a more definitive answer with some authority.
Like Daniela I researched this question without joy, so in the absence of any rules the best we can do is go with what sounds right and try and understand why it does. Taking Daniela's input as a guide I'll attempt an answer to my own questions.
When two adverbs follow a verb, can they be of mixed type, and if so is it commonly done?
It seems with the -mente form of adverb and the adjectival form this would sound odd. When you think about it the same is true in English. Unfortunately we have relatively few non -ly adverbs for examples, but consider "He ran strongly and quickly" versus "He ran hard and fast." In English we would tend to stick with like forms of adverb where possible (although mixing them would not be incorrect).
However, it seems the -mente form of adverb, or the adjectival form, can be coupled naturally with the phrasal "con + noun" adverb form. Again, the same is true in English. "He ran strongly and with speed" or "He ran hard and with speed": Either is fine.
If the adverbs can be of mixed type, and the first is a -mente form, does it still lose that suffix?
Apparently no, and this would make sense if we consider that the only different form of adverb that sounds natural after a -mente adverb is the "con + noun" form. As this is a prepositional phrase being used as an adverb it seems logical that the preceding -mente adverb should retain its suffix as it is not part of a -mente string of adverbs, but instead one adverb followed by a prepositional phrase (which just happens to form another adverb).
If we apply this logic to the original examples it gives us the 1,2,3 and 7 forms that Daniela suggests are most natural.
