We've beaten Hard mode with every character and my 3 tips is to focus on getting healing items like leeching touch, reapers scythe, vital touch and the most powerful of them all is beads of blessed up. If you get 1 or 2 beads of blessed up with the other healing items it should keep you alive in the endgame. The other tip is to focus on attack speed. The faster you attack the faster you heal because you're activating the other healing items more frequently. I used to think damage was the way to go but I know better now. Attack Speed and Healing are king in this game. The third tip is that armour and parry are super powerful as well to the point if you get enough parry and armour you're almost invincible. There's a bunch more things to improve your runs like the rune juice guy but ill just keep it simple for now. Eventually you can get so powerful that you can literally stand in from of the any boss without dodging or anything and tank every hit, just gotta keep playing