A potential customer wants this cake. Is it iced in buttercream or fondant? I am assuming it iced in fondant with fondant tweets/small sticks. I could be wrong. Your thoughts? Can this be done in all buttercream?

Not sure how the pic was made but looks like you could do a pretty similar look with buttercream, maybe rounding the top edge of the cakes to round them, then doing the random squiggles with a round tip.

Could be both. I would say iced in buttercream with fondant lines. Or buttercream and buttercream piping. 

Looks like fondant bc of the rounded tops, with RI piping?

ALooks like fondant to me..

 RF with piping.

Reminds me of some sci-fi horror film.

AWhat's rf?

Rolled fondant

AOh ok thanks :) so normal fondant... That's what I thought

The rounded shoulders of each tier suggest fondant, though it could be done in buttercream, but the raised lines can be either.  A piped line would be easier, and the breaks in the line suggest piping.  Fondant lines would require at least three hands, two to use the extruder and apply the lines to the cake and one to turn the cake on a turntable.