easy. i'm on Day 269 or something on level 1 only with extreme equipped. Yes, i'm using codes but the only one I used was to have all accessories so I could have extreme equipped
Leech was easy. Kill all but one of the tendrils, run into it to get down to limit-health, then kill it. Unleash limity hell on the now immobilised coffin. Heal using Cura, rinse and repeat. Two to three repetitions should kill it. The Leechgrave was definitely irritating, but only because I was playing a pirated version borrowed from my friend. It froze three times after I beat it.
Not including the bonus boss Dustflier, not really. Although there are some really annoying missions where you have to kill this nocture/Rasphody/Serenade-based heartless and all it does it fly in circles around the Lotus Forest with lots of health. I'll take a thousand Leechgrave freezes over another mission of that.