Alright, if there is one thing i know about necron is that you have to be kinda lucky to beat him in a short amount of time. It took me five minutes. Mainly because he used something called Blue Shock that is like Judgement sword (Brings one character down to 1 hp) And when he used Grand Cross, one person got minied or something. Just throw a dark matter at him, use shock, flare,ark, STRONG ATTACKS OF ANY KIND. It may take a while, but it works. And don't forget to heal constantly.