I just feel like:
-the FLUDD needs to automatically charge over time like ROB's laser
-the FLUDD should do hover mode in midair. Bonus to the occasional recovery, solid way to semi-spike foes
-the FLUDD should do low amounts of damage but not cause flinch, like Fox's laser.
-the FLUDD should not be aimable... there's not enough time to actually aim it and you'll almost always want to aim it directly to the right, so it's just a feature that ends up making it harder to use.
I actually would prefer a buffed FLUDD to the spin returning, it just seems more interesting.
And I want Luigi's vacuum to:
-replace the fireball special. The fireballs aren't particularly impressive and differentiating Mario+Luigi as much as possible seems good.
-be aimable.
-by default, sucks everything in-- enemies, projectiles, items, everything.
-when it sucks in a physical object such as a player or an item, the next push will eject it in the direction indicated.
-suck in elemental attacks (fireballs, ice blocks, electricity) and temporarily turn the vacuum into a cone attack.
It'd be nice to make the vacuum accurately represent the way it works in Luigi's Mansion.