Down B has slightly different properties on the ground
Role in the Subspace Emmissary
It turns out that Ganondorf was really somewhat behind the events of the Subspace Emissary when he was controlling the Ancient Minister (who is actually ROB being manipulated). He follows the orders of Master Hand and betrays Bowser by turning him into a trophy. It turns out however, that Master Hand was literally being a puppet of Taboo and was following the orders of Taboo, not Master Hand. Enraged, Ganondorf attempts to attack Taboo, but is turned into a trophy. He is later revived by Zelda and Link who points out what has happened.
Pros and Cons
High powered attacks, some of the strongest in the game (Forward Smash, Warlock Punch, Volcano Kick)
Some very quick attacks in the Thunder Jab, Up Smash, Up Air, and Wizard Foot
Forward B can commit Dorficide, evening the stocks
Dash attack gives boost of speed and hits incredibly hard
Down Aerial is still a very powerful spike, and can kill characters on the stage at moderate percents. If done immediately out of a short-hop, it can still hit most character's heads, but will finish in midair, leaving no landing lag.
Up Aerial has little landing lag
Very powerful ground game
Up B grabs with initial hitbox, and has powerful uppercut with later hitbox
Volcano Kick (Up Tilt) sucks people in
Most aerials have large landing lag
Forward and down smashes are slow to come out
Up Tilt is effectively useless for competitive play
Forward B can SD when you don't want it to
Recovery is not stellar
Dash A - Shoulder tackle. Gives Ganondorf a boost of speed as he performs it, and hits very hard.
Jab A - Lightning Palm. Longer in range and duration than his Melee iteration.
Down Tilt - Gannondorf squats on one leg and sweeps the other leg forward.
Forward Tilt - Gannondorf leans back a little and trusts one leg straight forward
Up Tilt - Volcano Kick, Similar to his Melee attack, Gannondorf lifts one leg vertical and holds it for a long time, before dropping it with a large explosion. A little faster than his Melee iteration with several distinct changes. Its hit is slightly less devastating and will not instantly kill at quite as low percentages. The downswing of the leg can hit, not just the explosion from it landing. It also has a "vacuum" property while charging, where any standing opponent in front of Gannondorf is sucked towards it (even if shielding), and any opponent standing directly next to Gannondorf will be pushed back slightly to the main hitbox of the attack.
Down Smash - Gannondorf squats on one leg, similar to his down tilt, and sweeps the other leg first forward, then back. Like Melee, the first hit knocks them in to the second. Unlike melee, this has a slightly more forgiving hitbox.
Forward Smash - Elbow thrust. Similar to his Melee attack and Captain Falcon's forward smash. Sends the opponent horizontally, like Captain Falcon's does, making this a lower percent killer.
Up Smash - Gannondorf does a high kick, lifting his leg to about thirty degrees from vertical quickly. Only hits once, unlike his Melee attack, and has more hitbox in front of him. Very fast attack, and can combo quickly and easily at low percents.
Neutral Aerial - Double kick, like Melee. Has less knockback, making it easier to land both hits, but harder to score a high-percent kill.
Back Aerial - Backhand, like Melee. Duration is slightly shorter, making this more like Samus's Back Air. Damage, speed, and knockback are similar to Melee's. One of Gannondorf's fastest aerials.
Forward Aerial - The Fist, like Melee. Swings his hand forward in an overhead arc downwards. High knockback, but not as high as Melee. Landing lag appears to be higher as well, as his fist sort of "sticks" in to the ground, similar to Link's Down Aerial.
Down Aerial - Thunder Stomp, like Melee. Appears relatively unchanged in damage, speed, and knockback. If done immediately after starting a (non-fastfalled) shorthop, the move will complete before hitting the ground, negating any landing lag.
Up Aerial - Overhead Flip Kick, like Melee. Appears very similar, except there is more knockback and range at the begining and slightly less at the end. Coupled with auto-sweetspotting, this makes it significantly harder to use for a reverse Up-air Spike, though this is still possible. Very little landing lag, and one of Gannondorf's fastest aerials.