I've stated before how I'd love to see a moveset based on the class change mechanic without having to switch stances to achieve this (as I tend to find movesets with stances/transformations/character switches cumbersome). This would pretty much mean he/she'd use different weapons for almost every attack which would be unique in it's own way. Though I have to admit it wouldn't be quite as interesting gameplay-wise as the stance/character change idea.
Well, let's see what I can put together:
Neutral B: Thoron
Robin throws the good' ol lance of thunder foward. It's a pretty basic projectile in that matter. To make things more interesting, here's an idea of how the skill could differ from your basic pot-shot ranged attack:
Add a short cast time and change the spell being cast based on where you tilt the analog stick during that time. This could run the risc of making a single attack way too versatile but with the channel period it would also leave Robin open for a quick preemtive strike or a evasive maneuvre. I'm sure there's plenty of cool ideas you could do.
Examples: Tilting up - Bolganone: lava erupts from below the enemy, launching them upwards. Tilting down - Flux: Dark energy pulls the enemy down from above (possibly spiking them with a sweet spot)
Side B: Ignis
Robin draws a sword, prepares to jump and does an attack based on how you time a second press of the B button:
No additional button press: Robin jumps foward (similiar to his/her Tactician/Grand master Critical/Skill Proc animation), imbuing his blade with magic mid-air and landing a hard-hitting strike.
directly after side B: Instead of jumping foward Robin fakes out, almost instantly firing a short range magic attack after which he/she dashes foward to further punish the opponent with the sword.
short pause before pressing B again: Robin makes the jump attack without magicly enhancing the weapon and instead casts a spell after landing a hit with the sword.
Up B: Rescue Staff
Lissa comes in riding a Pegasus, using the Rescue Staff to teleport Robin so safety. Once the Pegasus is on screen, it can be controlled slightly to adjust for a better angle or attack position.
This attack may be problematic because it's basicly another relatively large scale model that has to be created (unless it's also used in the Ultra Smash, which would make the effort worth it). Alternatively Robin could use the Rescue Staff him/herself though that wouldn't make much sense in terms of what the thing does in the FE series... And would also "just" be another teleport move.
Down B: Watch out!/Astra
Morgan (appropriately of opposite gender to the chosen Robin skin) jumps onto the battlefield, pushing Robin behind the enemy and blocking the attack. Robin immediately counter attacks by pulling out a sword and attacking five times.
Mechanicly, this is basicly just a fancier looking version of Marth, Roy and Ike's down B counter attack that hit's the enemy from the opposite direction. To put a bit more unique flare into it, Morgan always jumps in and pushed Robin. If no attack is blocked, Robin won't counter attack and stumble, leaving him/her open for an attack! Basicly a higher risk/reward version of the usual FE Counter.
I'll go into less detail with the A attacks, but they are quite important to get across what I wanted to achieve with the moveset (since the Special Moves all relied on Sword and Sorcery. Which was quite intentional.)
Side Smash: Axe
Robin does a spin attack with an Axe
Down Smash: Spear
Robin stabs diagonally downward with a spear, potentially impaling enemies on it, then smashes to the ground it in a wide swing above his/her head, sending enemies flying on impact.
Up Smash: Bow
Robin unleashes a flurry of arrows directly skywards. They quickly loose speed and rain back to the ground. They deal a decent amount of damage and knockback when they hit an enemy just as they are fired, but they quickly loose damage and don't have any knockback once they travel.
Side Air: Daggers
Robin does a few quick strikes with a dagger. While they technicly didn't exist as a seperate weapon type in Awakening, I still think it fits the character to have as many different weapon types as possible.
Down Air: Throwing axes
Robin throws a pair of throwing axes; one diagonally and one straight down.
Up Air: Lance
Robin stabs diagonally upward in both directions, then straight up.
Neutral Air: Arcwind
Robin is engulfed in magical wind, hitting enemies close to him/her multiple times.
Ultra Smash: Invisible Ties
The critical hit close-up from Awakening appears as Robin proclames: "Time to tip the scales!"
One after another several Awakening Characters come in and attack Robin's foes before jumping off-screen and making room for the next one to attack.
I imagined this order (presuming none of these would make it as Characters or Assist Trophies):
Chrom, Lucina, Morgan, Lissa, Tharja, Frederick, Vaike, Tiki
Of course that list is mostly arbitrary aside from Lissa and Morgan who'd already have models in the game from Robin's up B and down B. Tiki would make a good finisher and you have to cram Chrom and Lucina in if they don't make any other appearance in the game. Tharja, Vaike and Frederick are basicly just in to have a few more character styles represented.
Another possible list would be all the characters that have a special Beach/Hot Springs DLC image since that was based on a popularity poll at the time as far as I know.
Hm, after reviewing this I have to admit there's quite a lot of projectiles in the moveset, 2 of them even from A attacks... well, guess that stuff happens when you come up with the moves on the fly
I mainly wanted to get the Class Change and Pair-up gameplay features of Awakening across while still portraiting Robin as the thinking man/woman that he/she is.