We've already discussed Bubble Goth, so what's the difference with Pastel Goth?
Pastel Goth is simply just a style of pastel colours, with or without black. It is said to be a type of soft grunge, some say it looks like a creepy Fairy Kei fashion.
They are probably known as Kawaii Goth to some. It's more of a casual look with Gothic imagery such as bats, crosses, pentagrams, ect.
They wear pastel bows, little horns, round shades, pastel roses with spikes on their headbands. Usually their hair would be dyed pastel (or they wear a wig), it can be half black and half pastel if they choose.
Bubble Goths can also have pastel hair, but some may choose to dye it white, or bright colours instead. Pastel Goths are just have pastel and black, which is why they're called Pastel Goth. Their fashion is more Japanese inspired than Bubble Goth is.
Pastel Goth and Bubble Goth have similar accessories, like eyeball bows for example, (I have seen the Bubble Goth queen Kerli, wear eyeball bows in an interview), and the two has some Lolita in their fashion, but Bubble Goth has Cybergoth elements, whilst Pastel Goth does not.
Bubble Goths wear mostly platform boots, whilst Pastel Goths wear creepers, or more casual type of shoes.
The make-up is usually dark. Pastel Goths wear black lipstick for balance.
(Pics of Pastel Goth fashion from Google Images)