Getting no damage on monsoon took me a decent amount of practice, fought that ****er on revengeance for 3 hours straight only to discover that I had missed the ranked battle during raiden's emotional breakdown and had to do the chapter again. Other than that, I had trouble with getting no-damage on both Sam and the Senator as I went for the achievements during my second playthrough which was on very hard (i had no idea revengeance would've been significantly easier to pull no-damage for most of the bosses)
1. Monsoon no damage revengeance 2. Senator no damage very hard 3. Sam no damage very hard
Special Mention: The final checkpoint on sundowner, didn't score a high enough combo for an s-rank even with no damage, didn't backup my save, FML.
Monsoon by far for me. I had an easy time with most of the bosses but him. I just dunno what the hell you're supposed to do exactly to actually hit him or if you're just supposed to wait until the game lets you.
I didn't find Monsoon hard at all on my first playthough, his attacks were easy to parry and his non-hit phase was easy to plan for. Sundowner and GRAD however, were pretty tough my first playthough (on Hard)
Official Dark Samus of the SSB4 board SSB4 Roster: http://i.imgur.com/6Bta9nE.png PSN/NNID/Steam: Soanevalcke6