I don't know what this part in the below dialogue means.
It's an extract from one oh South Park scripts:
Stan:Hey, Cartman? How come the birthday invitation you gave me says 'Green Mega Man'?
Kyle:Yeah. Mine says 'Red Mega Man'.
Cartman:Right. That's what your supposed to get for my birthday.
Stan:Dude. You're not supposed to tell people what to get you for your birthday.
Kyle:Yeah, that's weak!
Cartman:Look, it's very simple guys. Green Mega Man goes with Red Mega Man and Yellow Mega Man to make the Ultra Mega Mega Man. You have to have all three or it doesn't work, see?
Stan:Up yours. Cartman. I'll get you whatever the hell I want. [crumples up the invitation and throws it away]
Cartman:Oooh. So maybe you don't want to have any of my mon's cake, pie, and ice cream, then.
Stan:Oh great, Green Mega Man it is. 

 In the context of the whole talk, what does this last phrase (by Stan) mean? 
It means that Stan really likes Cartman's mother's cakes and pies, so he has changed his mind and will buy Cartman Green Mega Man for his birthday.
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I know about this Emotion: smile But what is the grammatical or lexical rule of that"it is"at the end of the sentence? Could you give some other similar examples using this construction? Emotion: smile
It is a reasonably common formation:

A: What would you like for breakfast, dear?
B: I'd really love a poached egg.
A: Then a poached egg it is.

I suppose this is just an inversion of 'it is a poached egg (that you'll get)' for emphasis.
Thanks Mister Micawber! This is what I was looking for... I suppose Emotion: wink
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