Any BIG round tip. A 12 probably isn't big enough but I don't remember the #s of the super sized ones. Maybe something like a 1D?
Just start piping at the outer edge and circle into the center - raising up the tip as you go. I'd sure a rather soft b'cream - maybe add cream cheese to soften it?
You can also use just a coupler without a tip as long as it isn't a wilton coupler with the notch in it.
Looks to me like a pastry tip like the ones at Bake It Pretty:
I would say the details are fondant or gumpaste. You could cut out those eyes and cheeks with the small end of a round tip (I'd have to experiment to get the right size, but maybe start with 3 for the eyes and 5 for the cheeks), and the mouth is just a small ball rolled out into a snake. The cherry, of course, is just a red ball... maybe 1/2 inch in diameter... stuck on top.
This type of cupcake icing is becoming quite popular, eh? I prefer the 2D tip look, but with the cute fondant face, those cupcakes are adorable!
You can use a disposable piping bag and just cut the end to the size of hole that you want.