Krokodil is a cheap way of making desomorphine, which from what I've read is an opiate that's a few times stronger then heroin, and available by prescription in parts of Europe. There's nothing inherently dangerous about Desomorphine that sets it apart from other opiates, but with krokodil, people are basically synthesizing it in there kitchen, and what they end up with is a very unclean product, that's then injected.
From what I hear Desomorphine is stronger and shorter acting then heroin.
Anyway, there is lots of information on 'Krokodil' on the internet, including a documentary by Vice which is quite good. This isn't a suitable topic for OD though, unless you're considering using the shit, in which case; don't-just buy some smack.