El pulpo está muy bueno hoy.

Because estar is used for a current state or condition.

In El pulpo está muy bueno hoy, the speaker is talking about how the octopus tastes today, in this particular preparation or at this particular moment. That makes estar the natural choice.

• estar bueno = to taste good / be good right now
• ser bueno = to be good in a more general sense, or to have a good character

So está fits the idea of it’s especially good today.

Here it most naturally means octopus as food.

In Spanish, the same noun is often used for both:

• el pulpo = the octopus (animal)
• el pulpo = octopus (as a dish or ingredient)

The context makes it clear. Because the sentence says está muy bueno hoy, it clearly sounds like someone is talking about food.

Spanish uses articles more often than English.

When talking about foods, ingredients, or dishes, Spanish often uses el / la / los / las where English might not:

• El vino está bueno
• La sopa está salada
• El pulpo está muy bueno hoy

So el pulpo sounds natural in Spanish, even if English might just say The octopus is very good today or simply Octopus is very good today depending on context.

Here muy bueno means something like very good, especially in the sense of very tasty.

With food, bueno often refers to quality or taste:

• Está bueno = it tastes good / it’s good
• Muy bueno = very good
• Buenísimo = excellent / really delicious

It does not mean morally good here. It is about how the food is.

Yes, absolutely.

A very common alternative would be:

• El pulpo está muy rico hoy

In Spain, rico is extremely common for food and usually means tasty or delicious.
Both work, but the nuance is a little different:

• bueno = good
• rico = tasty / delicious

Both are natural, and native speakers use both.

Because that is a very natural position for time expressions in Spanish, especially when they modify the whole statement.

• El pulpo está muy bueno hoy
• Hoy el pulpo está muy bueno

Both are possible. The first one sounds very natural and neutral. Putting hoy at the end often gives a slight emphasis to today.

Normally, no. It sounds odd in this context.

Because hoy points to a temporary situation, Spanish strongly prefers estar:

• El pulpo está muy bueno hoy = natural
• El pulpo es muy bueno hoy = unusual / generally incorrect here

Using ser would clash with the idea of a temporary condition happening today.

Because it agrees with pulpo, which is a masculine singular noun.

Agreement in Spanish means adjectives match the noun in gender and number:

• el pulpo → masculine singular
• therefore: bueno

Compare:

• La paella está muy buena
• Los calamares están muy buenos

So bueno changes depending on the noun it refers to.

It is a predicate adjective used with estar.

Structure:

• El pulpo = subject
• está = verb
• muy bueno = adjective phrase describing the subject
• hoy = time expression

So bueno is still describing pulpo, but it comes after the verb because it is linked by estar, not placed directly before the noun.

Compare:

• el pulpo bueno = the good octopus
• el pulpo está bueno = the octopus is good / tastes good

It literally means today, but in real use it can imply today’s batch, the way it was prepared today, or how it happens to be right now.

For example, in a restaurant someone might say this because:

• the octopus is especially fresh today
• the chef prepared it particularly well today
• this serving tastes better than usual

So the sentence often carries the idea of a current, temporary judgment.

Yes, definitely. It sounds natural in Spain.

Especially in a restaurant or at the table, a native speaker might say:

• El pulpo está muy bueno hoy
• El pulpo está buenísimo hoy
• El pulpo está muy rico hoy

All of these are normal. The original sentence sounds like a perfectly natural comment about food.