My list of useless abilities:
Citron - Mood Shield
The Mood Shield lasts too short, so what's the point of actually using it if it lasts that short?
Corn - Multi-Shuck
His Multi-Shuck has too slow of a velocity, so why use it at all?
Cactus - Red Artichoke
It's nowhere near as good as the standard artichoke.
Superhero - Super Guided Ultra Ball
His Super Guided Ultra Ball is largely useless, because it's too slow!
Soldier - ZPG
His ZPG has too slow of a velocity to accurately vanquish a target especially while it's moving.
Scientist - Armored Heal Station
His Armored Heal Station does not provide a quick-enough health regeneration to anyone standing next to it.
All-Star - Shield Decoy
The Shield Decoy serves no purpose whatsoever; it's too weak, and only work as a decorative ability.