You should totally try Moonmoon.
If you haven't given Di a go already...
Be forewarned her early game is just as weak as Katarina's, but she scales nicely and can be built bruiser-ish (to not insta die like Kat if you're cc'd). She completely melts their squishies with 2 items, and continues to do so until game close (even if you trade a bit of ap for defense in games where YOU're getting bursted down
.)
However, she lacks the potential to rampage through multiple enemies like Katarina, and she also lacks a reliable escape if your engage fails. Her shield and interrupt (and the extra defensive items if you decide to use them) do help her survive the less favorable engages, though, and allow her to trade like a bruiser in many situations. If you're just making a disgusted face at the idea of a tanky assassin, building Di straight ap will of course allow you to shred whatever you jump on, but without the ability to slaughter multiple enemies at once or escape afterward...
She's mainly for taking out their backline (one unlucky lump of butter at a time) but she can headbutt a few tankier champions out of the lane, too. So whether you think you need super burst or sustain; BOTH are viable on her (which is beautiful). 1v1 just about anyone and you're set with Moonmoon (ofc if you're careful and don't get cc'd into your grave).
The only real downside I have to using her is her mana-hungry arse while laning against a ranged champ. Asking nicely for a blue usually fixes this though.~
So yeah, she's a bit weird, but I love the heck out of her.
I'll advise her to anyone :D
And ramble like an idiot (like this) repeatedly hehehe.