To start off, I'm going to talk about playstyle match ups with your partner.
I myself am have an extremely patient playstyle in Sm4sh and from what I have seen from my experience so far, I play well with other defensive players but not with offensive players. If I am playing a match in doubles with a random player who has an offensive playstyle, then we usually won't do so well. What will happen is usually I will get an early kill off of one of the opponents and then they will only focus on my partner. When this happens, I am forced to approach which is an option that can give my doubles character (Kirby) a bit of trouble. I will usually do well with a team mate that knows to run up and poke the enemies and then retreat and use me as a wall to cover him and get in hits while the other team is trying to deal with me. I will also do well with a partner who tries to stay close to me.
Now I want to talk about the playstyle/strategy of a team as a whole.
Once playstyle that I have used before is something that I call "Ice Climbers." It is basically when you and your teammate have similar playstyles and the two of you are doing similar things at the same time it is almost as if your to characters are a single entity. For example, sometimes when I play PM (Plz don't murder me for mentioning it here, it is only for an example) me and a friend would do doubles as Marth and Roy. We would play so similarly that we were like Ice Climbers with swords. An example in Sm4sh would be a team of villager's or a villager and another projectile based character setting up a wall of projectiles without hitting each other.
Another one that I mentioned before is the one where your team mate runs up and pokes the enemies and retreats to try and force an approach. In this one, your team mate acts like Falco's Laser did in Melee. You send them out to force an approach and they get annoying.
Now I want to talk about character match ups with my partner
I usually play Kirby in teams and my favorite partners are...
(I love this team mainly because you can get some sick Dair combos together and finish each other's uptilt combos)
And a heavy, usually
(I just love to swallow my team mate and spit them out at my opponent, they never see it coming. Also, the heavier the character, the more damage and knockback wjhen I sit them out at my opponent)
(Monado Kirby is God, Monado speed Kirby allows for easy Fair wall of pains, Buster Kirby can lead to inescapable (I think) Dair comboes. Also since armor Shulk is the heaviest character in the game, Spitting him out is basically a Falcon Punch with a moving Hitbox.
Please post your own playstyle MU's with partners, team strategies, and character MU's with partners!