Considering that Hydregion doesn't have the best defensive stats, accuracy and regaining life can really help. Like with Fire Blast, it's the only thing that covers your ice type weakness, so you want accuracy to be pretty high. So a Wide Lense will be your best bet for that.
Another option would be to get a brightpowder and make the opponent miss you. It can really make a difference in a battle.
And my last suggestion is a Leftovers. Get all the life you can and, like accuracy, it can really make a difference.
Hope this helps =)