Gelyan + Nidhogg is pretty amazing, just put points in power, endurance and empathy and grab arcane earrings; toss up solar eclipse and take as much damage as you can while staying alive, and you will never run out of energy. I beat Nightmare Zodiac Memory this way and only used one soul refresher the whole fight.
(this only applies to HC mode once you have all the other medals) I have played this game a lot and my favorite composition is a rogue as my hero and a noble either two rangers or a ranger and a militia as my employees. Grab a revolver as soon as you can and hold down space to put it into auto-reload mode. Max out power shot, sense, killer and luck first. Once you get to higher levels make sure to put a lvl 3 anti-air mod and fire rate + damage mods when you can; after you have a good fire rate mod start putting points in aimed shot. Put grav guns on everyone else and you'll have no problem getting to 100 days on HC.
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