Doubles is not separated 1v1s, that's usually the first thing people try to do when they first try competitive doubles, and sometimes you do have to do that, but is not how it should be played often. You ideally want to force a 2v1 situation and wall out the other opponent teammate.
I'm assuming team attack is on.
Fast characters like Inkling, Fox and Pichu who can creat oppenings or force reactions are good in doubles.
Cloud is still really good in doubles. Though the way he was toned down will make him less centralizing than in S4, but that's a good thing. Limit attacks are still very powerful and despite his sword getting nerfed he still manages to control space well enough.
He has been talked about too, but Little Mac does well since he can have a teammate cover his back and greatly complement his weaknesses of having poor aerial presence and linear approach. He still has those weaknesses though so he can struggle quite a bit if his teammate gets clobbered.
I know there's a Ness/Lucas + projectile character combo too. Lucario in particular doez extremely well together for the aura providing even more health to the Mother boys.
There's G&W with his bucket as well and he can absorb his teammates own projectiles with it to make a powerful attack.
Villager and Isabelle finally can do some fun stuff with pocket. A Snake can team up with them and feed them an Upsmash missile that they can pocket to make much stronger when they throw it out. Villager can chop his tree down and have a teammate Fox reflect it, then immediately pocket it to store a grossly powerful attack.
