http://www.slate.com/blogs/browbeat/2014/03/17/_let_it_go_watchmen_mashup_does_let_it_go_pay_homage_to_the_dr_manhattan.html
There's even a vid:
It looks like there were others that have had their sound tracks muted due to takedown notices from Disney.
It's a shame that nobody seems to have done it the other way, with the Watchmen music etc. on the Frozen footage.
And if I haven't recced it before, there's a fun Frozen / Thor crossover fanfic series, in which Loki is Elsa's father:
The Ice Demon By Lizardbeth
http://archiveofourown.org/series/148596
Currently five stories and 164K words.
