kizzie, they had a few character clothes - can't remember which though! - in M&S at the weekend in the sale too. if you have one close, you could try ringing them to save yourself a journey and they might 'bags' it for you.
SueDonim I shall no doubt be back in Asda over the next couple of days and will have a look for you. They have dinosaurs so mermaids don't seem too out of the question. DD has previously had a mermaid from there too. Still got it somewhere but she complains that the bodice itches.