I have been asked to do this Turbo cake and am completely clueless when it comes to the construction/support of 3d cakes.  Any help would be greatly appreciated!  Thanks!

ABall pan for the body or carve the cake into a ball shape. RKT for the head.

That's what I was thinking but how would I support the head/neck when it's just RKT?

I think I would model the RKT around a stick support, plus 2 toothpicks for the eyes. You could use dry spagetti (the kind that is actually a little tube, don't remember what it is called) instead of sticks. I use them for flowers, so it is all edible.
 

ASorry to bump in, but I was wondering, how would you cover of fondant the snail to have a nice and smooth finished? Isn't too long and narrow?

AIf you use modeling chocolate you can rub the seams together.

hi I wanted to know if you managed to do the cake did the structure of ball cake and rkt work coz i need to make one for my nephew too

If the nech and head is RKT I would say it definitely needs support.I let mine go really hard before covering in ganache. And then let the ganache go really hard before covering with fondant. Even then I would want a support inside a neck like that.....perhaps a dowel or rod fixed into the board. With regards to the fondant...if it's good quality and soft enough it should be plyable enough for the seams to be rubbed together. A hot pallette knife (heated in boiling water then dried) helps to merge difficult seams. But the quality of the fondant is important.

My Nephew Wants me to make this 3d cake for him next week can you tell me how you constructed the fin in the back and how did you put it together so it wouldn't fall apart Thank you in advance

Molly2