I've gotten every skin possible from hextech crafting via re-rolling skin shards. Then I went through and made a list of the skins you can not get.
They are as follows:
Urf the Manatee Warwick
Riot Squad Singed
PAX Twisted Fate
If you think I missed something please let me know!
Post feedback on your impressions of the PBE experience here.
Feedback regarding the PBE Community site lives in the [Site Feedback subcommunity](http://community.pbe.leagueoflegends.com/c/site-feedback).