In my opinion there are plenty of underdeveloped characters with more potential, some being Peach for her Turnip game fully tapped, and Sheik for her many under used moves.
Though the one which I think is the most underdeveloped with serious potential is Samus. She has all the tools to become a S tier character, varying from an insane Crouch Cancel (allowing good punishes), very heavy weight ( survives much longer), extreme floatyness (making getting combos on her very difficult, survives horizontal attacks much longer, and most importantly kills many grab throw set ups such as Fox's up throw Up-Air), amazing recovery (so good it's better then many smash 4 recoveries xD), a good wave dash, crazy good tilts (which hit hard and plenty of range), viable smash attacks (more specific her down smash, which is faster then most tilts, and hits very, very hard, while suffering close to no ending lad), extremely versatile aerials (With the single hit aerials allowing for plenty of range. knock back and a continuous hit-box; with the multi hit aerials seeming to be unbeatable, while extending combos). Up-B (has 2 frames of invincibility, making Up-B out of shield safe, while killing many approach options), Down-B (as well very versatile, it is used for recovering, eliminating approach options, edge guarding, and gimps), Neutral-B (AKA charge shot is a good 25% dealing, hard hitting kill move that is fairly fast), Side-B (her missiles -again another versatile move- has many uses, some being edge-guarding, approaching, and suppressing approach options), a wall jump (a rare feature for floatys that extends her capabilities), and don't even get me started on her leash.
In all Samus is an extremely versatile character, who has tools for virtually everything. Sadly she is shied upon do to her poor roll, and some what slow grab.
