Ah doubles! They are so much fun even though I absolutely suck in them. I have somewhat limited experience with doubles, but I have played enough to make some judgements about my main:
The King is so much freaking fun to play in doubles. The main things to talk about here that differentiate doubles and singles for Dedede are his size, his offstage abilities, his speed, gordos, and inhale.
Size: Dedede is extremely prone to getting hit a LOT in doubles because he is so big. Sometimes its very difficult to even avoid your teammate's attacks due to Dedede's size and speed, especially characters like Ike with big hitboxes. This means you will take a lot of damage quickly if you are in a bad position and your teammate cannot help.
Offstage: Dedede is great offstage, which is extremely important in doubles. Dedede is almost impossible to gimp, and when recovering low gets almost free passage back to the stage, which is great versus many popular doubles teams. Also, Dedede shines when he can be constantly edgeguarding people. He can rack up a lot of damage from an edgeguard or get a kill, even when facing two people at once on the ledge, he is capable.
Speed: Dedede has a very poor ability to help out a teammate in trouble. He just can't get to the other side of the stage in time. Chucking a gordo across the stage can sometimes save your teammate, or sometimes make matters even worse. Also with how large and reckless Dedede can be with his hammer, it becomes hard to hit an enemy when they are close to your teammate without hitting everyone, so Dedede is very bad at bailing a teammate out.
Gordo: Gordo becomes especially interesting in doubles, as your teammate can hit it towards enemies if it is out, and it can hit multiple enemies with a single gordo if they are close. Making a stage hazard like gordo in doubles can be extremely valuable when your teammate can work around it, as you can work together to completely take control of the entire stage between you two and the gordo, which creates some very advantageous and rewarding situations.
Inhale: Inhale becomes really cool as you can spit an opponent into another opponent, or even use your teammate as a projectile and help them approach at the cost of 10%. The star created by spitting someone out kills reasonably well too, and can be used to style on your opponent with extra pizzazz!
Good partners: anyone that can take stage control and throw people offstage, preferably fast, precise, and able to manipulate gordo well. Edgeguarding, KO power, and damage racking are not required.
I may post about Charizard later. Depends on if I have time.