In "Twelfth Night", what does Malvolio fancy himself as?
"You are sick of self-love", Olivia tells Malvolio, "and taste with a distempered appetite". And he is: he genuinely thinks he is fantastic. So before I tell you the things that Malvolio fancies himself as, I could just tell you that Malvolio fancies himself. He does.
Maria, in Act 1, Scene 5, gives a pretty good analysis of his character:
The devil a puritan that he is, or any thing constantly, but a time-pleaser; an affectioned ass, that cons state without book and utters it by great swarths: the best persuaded of himself, so crammed, as he thinks, with excellencies, that it is his grounds of faith that all that look on him love him; and on that vice in him will my revenge find notable cause to work.
Malvolio is not a puritan (it's not about religion), nor does he do anything constantly. But he changes his mind constantly, according to the fashion of the time. So he fancies himself fashionable.
He also fancies himself as an intellectual: he learns quotes from books by heart and quotes them back.
And lastly he also fancies himself as hugely attractive. He thinks that everyone loves him. And we all know people like that!
There's one more thing. When he comes into the gulling, Malvolio is dreaming aloud:
To be Count Malvolio!
Malvolio fancies himself as an aristocrat: as someone worthy of being a count. And that's key to why he wants to believe the letter so much: it'd bump him up a few rungs.
Hope it helps!