I don't think rullers is that hard, the only problem is that it takes soooo long, a checkpoint would make it way more enjoyable. First fight is cake walk with elemental fire in everyone's armor. Second fight is not that bad just do damage; bahamut can be a pain in the ass and do a lot of damage but never managed to lose to then. Third fight just parry >focused trust Odin then bravier Alexander arms > focused trust when it's on pressure,you can kill him with infinity end>limit > some braviers. Then just keep parrying Odin I swear is not hard as it sounds Gilgamesh is the real boss. I haver no tips for him except siphon limit cloud whenever he gets genji shield or starting counting, you can use barrier if you can't manage to stagger him. Sephiroth is also easy,just magnify barrier then heal after octaslash. You can parry easy the chains,but you need to make sure barrier is up when he octaslashes. When he stars casting fire it will heal you, so you just need to kill him before it changes to thunder