La piedra tenía musgo y estaba muy resbaladiza.

Yes. In Spanish, tener is often used for visible features or things something is covered with or has attached to it.

So La piedra tenía musgo is a natural way to say the stone had moss or had moss on it.

Other possible versions are:

• La piedra estaba cubierta de musgo = the stone was covered in moss
• La piedra tenía musgo encima = the stone had moss on top of it

But tenía musgo is perfectly normal.

Tenía is the imperfect tense, and it is used here because the sentence is describing a past situation, not telling us about a completed event.

The stone’s moss is part of the background description:

• it had moss
• it was slippery

If you used tuvo, it would sound more like a completed, bounded event: the stone had moss at some specific moment or somehow came to have moss. That is not the usual idea here.

So:

• tenía musgo = it had moss / it was mossy
• tuvo musgo = it had moss at a defined time, which sounds less natural in this context

Spanish often uses estar for a state or condition, especially one that is true in a particular situation.

Here, muy resbaladiza describes the stone’s condition at that moment: it was slippery.

So:

• estaba muy resbaladiza = it was very slippery in that situation

If you said era muy resbaladiza, it would sound more like you are describing the stone as inherently or generally slippery, almost like a characteristic.

In this sentence, estaba is the most natural choice because it describes how the stone was then.

Because both parts are descriptions of the scene in the past.

The imperfect is commonly used for:

• background information
• ongoing states
• descriptions
• circumstances around another action

This sentence sounds like scene-setting:

• the stone had moss
• the stone was very slippery

It does not present either idea as a single finished event.

For example:

• La piedra tenía musgo y estaba muy resbaladiza, así que me caí.

Here, tenía and estaba describe the background, while me caí is the main event.

Because adjectives in Spanish usually agree with the noun they describe.

Piedra is:

• feminine
• singular

So the adjective must also be:

• feminine
• singular

Forms:

• resbaladizo = masculine singular
• resbaladiza = feminine singular
• resbaladizos = masculine plural
• resbaladizas = feminine plural

So:

• el suelo resbaladizo
• la piedra resbaladiza

Because muy is used to modify adjectives and adverbs.

Here, resbaladiza is an adjective, so you need muy:

• muy resbaladiza = very slippery

Mucho is used in different ways, usually with:

• nouns: mucho musgo
• verbs: resbala mucho
• comparisons or quantities

So:

• muy resbaladiza = correct
• mucho resbaladiza = incorrect

Because musgo is being used here as a mass noun in a general sense, not as a specific, already identified patch of moss.

So tenía musgo means:

• it had moss on it
• there was moss on it

If you said tenía el musgo, it would usually suggest the moss is a specific, known moss already mentioned in the conversation, which would be unusual here.

Compare:

• La piedra tenía musgo. = The stone had moss.
• Quité el musgo de la piedra. = I removed the moss from the stone.

In the second sentence, el musgo refers to a more specific thing.

That depends on context.

La piedra suggests:

• a specific stone
• a stone already known to the speaker/listener
• a stone that is identifiable in the situation

Una piedra would introduce it as a new, non-specific stone.

So both are possible, but they mean slightly different things in context:

• La piedra tenía musgo... = the stone had moss...
• Una piedra tenía musgo... = a stone had moss...

In isolated example sentences, Spanish often uses la when talking about a concrete object as if it is already in view.

Because Spanish usually drops subject pronouns when they are not needed.

The verb forms already tell you the subject is third person singular:

• tenía
• estaba

And since the subject is already mentioned as la piedra, Spanish does not need to repeat ella.

So this is normal:

• La piedra tenía musgo y estaba muy resbaladiza.

You could say ella estaba muy resbaladiza, but it would usually sound unnecessary unless you wanted special emphasis or contrast.

Yes. That is grammatically correct.

Changing the order changes the flow a little, but not the basic meaning.

• La piedra tenía musgo y estaba muy resbaladiza.
• La piedra estaba muy resbaladiza y tenía musgo.

The first version may feel slightly more natural if you want to present the cause-like detail first and the dangerous condition second. But both work.

Spanish word order is fairly flexible, especially in a simple descriptive sentence like this one.

Yes, resbaladiza is a standard and natural word in Spain.

Some related options are:

• resbaladiza = slippery
• deslizante = slippery/sliding, often more technical or formal
• resbalosa = common in much of Latin America, less typical in Spain

For a stone in a natural setting, resbaladiza is a very good choice in Spain.

You could also rephrase the idea:

• La piedra tenía musgo y resbalaba mucho. = The stone had moss and was very slippery / you could slip on it easily.

But estaba muy resbaladiza is more direct and descriptive here.