Kirby + R.O.B. Team
Team Synergy
These two partner so well together because of a number of factors. The first is the fact that ROB has trouble getting KOs at low to moderate percentages. With Kirby, the team's KO potential goes up quite a bit since Kirby's F-smash, Hammer, Giant Swing, and Stone are all much easier to land than in 1-on-1.
Another benefit is the fact that ROB is a heavy character that is hard to kill. Both he and Kirby have an easy time recovering off stage, but ROB is even more resilient with his ability to survive to higher percents, Meteor Cancel with ease, and fly back to the stage from practically anywhere. In addition to this, both ROB and Kirby can assist each other in recovery by attacking edge guarders or boosting their parter with attacks should Kirby be out of jumps or ROB out of fuel.
Finally, ROB covers an important part of Kirby's weakness and that is short range and poor priority. ROB can take on opponents that Kirby might have trouble with and leave Kirby to take care of easier match-ups; these include Marth, Snake, and Olimar to name a few. Kirby in return has an easy time staying out of ROB's way with his small stature, quick hits, short crouch, and evasivness. This allows ROB to fight with a good deal of freedom.
Team Tactics
For the most part, this team will be breaking off to fight individually but this does not mean team tactics are not a very important part of the overall strategy. Even while fighting separately, it's important for both ROB and Kirby to watch each other's back in case one or the other gets into trouble. For instance, ROB is susceptible to Dedede's chaingrabs and will need Kirby's help in breaking out and taking as little damage from a grab as possible.
Breaking grabs with both ROB and Kirby is a very important technique. Kirby will want to use a quick hit that deals little damage and/or disrupts the opponent greatly. What you do NOT want to do is run in and break the grab with a strong hit - if you use something like a Smash Attack you'll be dealing as much or more damage as the opponent's throw, might KO your partner, and leave yourself lagged. Instead, use your tilts, a Jab, or if you're far away you can go for Dash Attack or a Final Cutter shot. Likewise with ROB, don't use things like F-smash or full-charged Gyros. Just walk up and jab or tilt, or send a laser at the enemy if you're far away.
Both players should learn what their partner's attacks do and how to follow-up on them without getting in the way. For instance, Kirby's D-air can lead right into an attack from ROB, but ROB should know that Kirby can follow-up his D-air with a Grab, F-smash, or Dash Attack. This means that the ROB player should have something worked out with Kirby ahead of time so he assists the D-air instead of getting caught up in the follow-up or messing up Kirby's follow-up. For instance, ROB could jab someone out of Kirby's D-air to force them into Kirby's F-smash, or he might charge his F-smash while Kirby runs in, Grabs and holds them in place.
Kirby can combo out of a lot of things that ROB does too. ROB's combos are fairly limted, but Kirby can work off ROB's D-throw, U-throw, D-smash, U-tilt, N-air and F-Special. Situational combos can also be pulled off with such things as ROB's D-air spike sending an opponent onto the stage right in front of Kirby to Jab lock or F-smash/Hammer.
Some of the most obvious team tactics revolve around grabs. ROB grab-releaseing into Kirby's Hammer will KO most anyone at around the 90% mark. Things get a little trickier when Kirby's the one doing the grabbing since ROB's KO options are fairly weak, but at high enouh percents a grab-release into ROB's full-charged F-smash could do the trick, as can a D-throw into ROB's N-air. You can also try a F-throw into ROB's U-smash, though the spacing is a bit tight. If you're in a 2-on-1 situation you have a lot more leeway and can usually just Grab-Release from Kirby to ROB and then finish the opponent off with a charged Smash Attack or Hammer.
Some 2-on-1 options to build up damage on the opponent's fresh stock include "Locks". To start one, either F-throw with Kirby into ROB's D-air, or D-throw with ROB into Kirby's Footstool. Both Kirby and ROB have an attack that locks a downed opponent, ROB can D-tilt Lock, and Kirby can either Jab Lock or D-tilt Lock someone. Once locked, you can continually hit the opponent to the edge of the stage at which point Kirby can grab the opponent, dangle them over the edge, and ROB can jump out and spike them with a D-air. Kirby's spikes aren't as powerful, so most of the time it's better just to let the ROB do the spiking, but if you want to do something with Kirby instead you can go for either a Grab-Release, or ROB's U-thow/D-throw into Kirby's Inhale for a Kirbycide, or maybe into his D-air or Giant Swing.
Copy Options
Kirby has a great advantage when teaming with ROB in that he can get one of the best Copy Abilities in the game from his partner. ROB lasers are great in many situations, but you have to be careful when using them. If you just throw them out randomly you have a good chance of messing up your partner's offense/defense. To use lasers prudently is to use them sparingly.
A great time to use your copied lasers is when an opponent is off the stage. You can disrupt their recovery and build damage without fear of hitting your partner (assuming he's not out there also). When fully charged, ROB's lasers can also send a recovering opponent off the screen for a KO - it's possible to do this without a fully-charged laser, but it's much less likely to happen.
Use lasers with your own recovery. Kirby has so many jumps that he can afford to fire off a laser (or two) while making his way back to the stage. Your partner won't be so upset if he happens to get hit by one of these since you're struggling to make it back alive.
Angle your lasers up and down, and bounce them off whatever slopes you find. Not only does this make it harder for your opponents to guess what angle you're fire from, but you can also angle the lasers away from your partner to bounce it around him and hit nearby foes.
Lasers are so fast and reach so far you can use them to help out your partner from across the stage. When your partner is caught in a combo, or is in a grab, send out a laser to disrupt his adversary and help him out. Watch how ROB uses his laser to find out new or interesting things to do in doubles.
Not having Lasers is also an option. Keeping your Inhale ability is always useful in teams for Kirbycides or to use against Shields. Spitting one opponent into another with Star Shot is always amusing and useful, and you can even use ROB for ammunition too! He's a heavy weight and deals strong damage as a Star Shot attack (15%), which can net KO's on light weights at higher percents.
Match-ups
ROB and Kirby do especially well against characters who have trouble with recovery or are easy to KO. Disjointed attacks can give them both trouble, Kirby moreso than ROB. Some difficult characters include Snake, Meta Knight, Mr. Game & Watch, Wario, and Marth.
Characters that normally give either ROB or Kirby trouble in 1-on-1 are actually easier with 2-on-2 due to several factors. With Kirby, the added number of opponents makes it easier to get in close and fight, as well as creating a lot more openings for his stronger hits to get in. This makes fighting Snake, Meta Knight, Olimar and Marth easier, though it can still be a difficult situation for Kirby. For ROB his match-ups get easier because his attacks come out quickly and separate people making it easier to disrupt the opponent's team and catch players by surprise. This makes fighting Mr. Game & Watch, Meta Knight, Dedede, and Falco easier since he doesn't have to worry so much about making mistakes and getting severely punished, can go for gimps easier, and has a teammate to aid in KOs.
Overall, this team is fairly effective. The drawbacks include Kirby's light weight and short reach and ROB's lack of finesse (bulky attacks and slower speed). The advantages include great recovery, great off-stage game, and good close-quarters fighting.