(Potential spoilers) Win the final round without being KO'd?

[HenryXLII]

So I just did the final phase of the World of Light true final boss without losing a stock. It took a few tries, but I managed to down them both after enough persistence. Yet despite not losing a stock, I did not get the achievement for "Win the final round without being KO'd". What exactly did I do wrong? Do you have to win the final phase of your first try without losing a stock? Or do you have to win THE WHOLE battle without losing a stock? If the later, that sounds somewhat annoying since it is a really long battle, and I might have to turn the difficulty down to get it done, or resort to autoheal.

 

[ChikoLad]

I stupidly lost a stock on the final round by falling off. I then quit, pressed "rematch" to reset the final round, and then did it again without losing a stock. Didn't get the achievement.

Tried it again and didn't lose a stock for any round. Got the achievement. Did it on Easy too since yeah not doing that one on Hard, bosses are too tanky on Hard and the very last boss is a mess on Hard.

I recommend using Gold Mario Spirit, he takes three slots but gives you Super Armour without any movement penalty.

 

[Wiinner159]

From how I understand it, you can't lose a stock period, and selecting rematch doesn't work to get the achievement.
I did it on Normal and my strategy was to use a lifesteal spirit like MM Skull Kid and attached with it some health regen supports like meloetta or manaphy. Should keep you pretty low damage for most of the whole battle, and as long as you understand the other bosses moves in the rush you should get out of that relatively unscathed when it comes to the final battle.
With that fight I played it's safe and kept distributing my damage evenly between the two, that way I could get the "dizzy" state department happen one after another so I could get a solid amount of free damage (helps especially when you get it where one of them won't do that attack on the other until just the end of the knockdown time, prolonging the damage you can do to them. At around half health is the dangerous part, stay away from Mr Eyeball (not naming specifically for spoilers) since when he brings out his gun attack you can easily rack up over a hundred damage within seconds and since this is when they pull out the most devastating attacks it's crucial to remain low percent. At around 25% health I targeted one of em to make it easier on me and there's the homestretch. Just be patient and only attack when it's safe and you should be good.