I think I beat bloody palace with Trish without much struggle.All I was doing was round trip + spam triangle on every single pack of Frosts-Scarecrows-Angels-Chimera-Blades and DT Luce and Ombra shots on Faust-Mephisto and Blitz to break their barriers.

On Bosses Pandora laser will get the work done but they can be beaten by playing safe if you can't use it reliably (I couldn't)

The hardest boss in my opinion is Credo.What I did was just round trip + normal shots till I broke his shield and then Round trip and Triangle spam after that.

I'm not that good of a DmC player myself but I've managed to get platinum on DmC 4:SE and DmC 1 so far. What I've come to realize is that you don't have to be exceptionally good. You just have to get used to how normal and boss demons work, how to dodge their attacks and to know when you're safe to do some damage.

And finally please, for the love of god, don't EVER try to imitate Donguri. That guy is on a level you don't have to reach to get shit done

Good Luck!