•Rayquaza was a boss in brawl, but in time isn’t as popular as he was. However, he worked well as a boss in UNITE and is supposedly going to have a major role in the new anime. But overall, Rayquaza isn’t really a villain.

•Giratina could have been the boss in brawl, however they chose Rayquaza instead. This however, was before platinum, which was giratina’s biggest role. Not to mention the how legends: Arceus came out last year, and giratina would be an iconic choice.

•Necrozma is definitely boss-fit and a true villain, however, gen 7 might not be iconic enough.

•Eternatus could utilize it’s eternamax form and it’s definitely a good one for a smash boss, but sword and sheild, I feel, might be overlooked in smash 6.