I like Elwind's customs, there fun. I will agree with Nos though. However, I would like Thoron+, if it didn't charge so slowly. I also like Arcfire+ as an Edgeguarding tool, seeing how much further it goes than normal Arcfire. What you combination with Robin's custom anyway?
My combination 90% of the time is:
Thunder+
Fire Wall
Default Elwind
Default Nosferatu
In match-ups where we get zoned out by the other's projectiles (like, DHD for example):
Thunder+ (Sometimes Speed Thunder in specific cases)
Arcfire+ (The long-range Fireball)
Default Elwind
Default Nosferatu (Sometimes Long-range Nosferatu)
In general, I think Fire Wall is
extremely powerful when it comes to zoning out opponents (especially fast characters), and is immensely valuable in helping Robin get back down to the ground safely. Shoot it at the ledge as you fall towards it, shoot it inbetween you and your opponent to claim space.... it has so many uses.
I take Thunder+ almost all of the time because I believe that Thoron++ (hold the button) is probably Robin's single most important killing tool.
That special changes how your opponents have to handle Robin.
It makes them feel pressured to approach you, because they don't want to let you charge it for free.
It makes you extremely threatening on stages where you can run away to charge it (Ferox, Prism Tower at times, Reset Bomb Forest).
ANY laggy move or reckless approach can be punished by Thoron++ for 33 damage, which often outright kills once they're at 60% or so.
It traps landings AMAZINGLY well because of how long the beam stays out. If your opponent burns their double-jump and you fire it into their path with correct timing, they have to up-B away from it or die.
It traps TECHS, too! If your opponent is in tumble, you can shoot it as they land (whether they neutral tech, hard land, or tech-roll), and it will meaty them and catch ALL of their options.
It's too good. Way way too good.