Fox + Ness would be a terrible team if they used strats like described from Foxy Sigma (no offense). If Ness is ever using his Up+B to help fox recover, he will most likely die himself i.e. fully charged usmash, falcon punch, ganon's neutral B, rest, ect. Ness dies easily enough but just chillen there asking to die, not a very good idea.
If ness tail whips fox back to the stage, then ness will just be gimped because of how bad his recovery is. Although the laser spam to heal ness is a good idea, it will not be often that you two have kill both people at the same time, even so you only have a few seconds IF you are already in position. Indeed Ness and Fox do both have nice KO smash attacks, ness dies at very low percents and if he's off the edge, it's just too easy to gimp his up+b.
All in all, the team can be good, but not from the reasons stated in the previously made post.