You yourself - double pronoun

You have made it up yourself.

This is obviously ok. But if the pronoun it should be repalced by a long noun-phrase:

You have made up the illusory world in which you move yourself.

It would sounds very ambiguous and will be misunderstood.

But can this be correct?

You yourself have made up the illusory world in which you move.

Is it considered "good" English? Can it be used formally? If not, why? And what are the alternatives?

You yourself is perfectly grammatical and idiomatic. It is used for additional emphasis. The Corpus of Contemporary American English has 475 cites for it, and the British National Corpus has 137. But since these two naked numbers alone mean little, here's putting them into some perspective:

                  COCA       BNC

you            3556382    661498
yourself         48157     10229
you yourself       475       137

he himself        1956       724
she herself       1075       365
I myself           996       191
they themselves    914       295
we ourselves       321       100

them themselves     54        23 
me myself           18         2
him himself         12         8
her herself         11         2
us ourselves         7         0

1.) You have made [it] up yourself.

2.) You have made up [the illusory world in which you move] yourself.

3.) You yourself have made up [the illusory world in which you move].

Your versions #1 and #3 are demonstrating the emphatic use of a reflexive pronoun ("yourself") -- which is part of standard English.

But in version #2, the reflexive pronoun is not being used in that way. Instead, that pronoun is now a direct object within the relative clause "in which you move yourself". (This is because the particle "up" does not separate the matrix clause object from the reflexive pronoun "yourself" as it does in version #1.) And so, version #2 has a different meaning from the others.

QUESTIONS: Is it considered "good" English? Can it be used formally? If not, why not?

I'm assuming you are asking about the emphatic use of the reflexive pronoun: this is probably more of a style issue, and I'd guess that some of the more formal styles and registers might not care too much for it.

QUESTION: And what are the alternatives?

As to your question for alternatives, you could try postposing the heavy direct object, or use dislocation (left or right), though if you try one of these or other information packaging constructions you might also want to consider moving that reflexive pronoun to another slot. (Also, be aware that dislocation is often considered more appropriate to an informal style.)

For instance, postposing,

• 2.b) You have made up yourself [the illusory world in which you move].

And left dislocation,

• 2.c) [The illusory world in which you move], you have made it up yourself.

And right dislocation,

• 2.d) You have made it up yourself, [the illusory world in which you move].

though, note that for right dislocation, that there are constraints, such as: the dislocated phrase must represent discourse-old information (CGEL, page 1412). This means that the info of "the illusory world in which you move" must already have basically been mentioned earlier in the prose.

Superficially similar to right dislocation is the construction extraposition which happens to allow the extraposed constituent to be discourse-new information. But noun phrases in general tend to resist extraposition, e.g.

• 2.e) You have made it up yourself [the illusory world in which you move].

but this (#2.e) is probably ungrammatical. (Notice that #2.e has no comma.)

You could also try complement preposing,

• 2.f) [The illusory world in which you move] you have made up yourself.

But for preposing, it too has constraints, such as: the complement must be discourse-old, acting as a link to other entities evoked in the prior discourse (CGEL, page 1372).

You can also move the emphatic reflexive pronoun around. For instance:

• 1.) You have made it up yourself.
• 1.b) You yourself have made it up.
• 1.c) You have yourself made it up.

You can also try other information packaging constructions. For instance, the it-cleft:

• 3.b) It is [the illusory world in which you move] that you yourself have made up.

• 3.c) It is you yourself that/who have made up [the illusory world in which you move].

Hopefully this is what you were asking for.

I happen to have come across this by accident but must comment on the thread even though it is over two years old!

Shivadas’ suggestion of “You have made up the illusory world in which you move yourself.” is indeed ambiguous but, if anything, it emphasises that you move yourself in the world which you – happen to have – made up.

On the other hand, “You yourself have made up the illusory world in which you move.” is grammatically correct and emphasises that it is you who made up the world in which you – happen to – move (which was, I believe, what was intended and which agrees with the first sentence “You have made it up yourself.” mentioned by Shivadas at the beginning of the question).

Terpsichore’s suggestion of “You have made up the illusory world in which you yourself move.” does not have the same meaning at all but incorrectly stresses the movement rather than the making up just as in the other sentence with "yourself" at the end.