When I was going for the Advanced Slayer trophy, I did my tries with both the Blessed Gun and Rainbow Run modifiers active. This helped me a lot. Since my gun was frequently changing due to the blessed gun, I could always got for passive/active items from the Rainbow Chests at the beginning of each floor. Sometimes, I would roll the Weird Egg which meant I didn't have to go through the Rat's layer (if you drop it in fire, it will hatch - feed it 4 junk)
You'd end up with runs where you pick up a lot of good passives and you're really strong. With this set up, I eventually had a run where I had really good items (especially clone) which helped me breeze through the game and comfortably beat the Advanced Dragun.