Top Tier:
Rationale: Both characters have very gimpable recoveries (especially Fox), will be hit by both dtilt and ftilt if they don't tech a Flame Choke, you can kill Fox ridiculously early out of a misplaced side b, and you can actually jump over PK Fire with default Wizard's Foot.
Notes: I think Ganondorf does slightly better against Meta Knight than the rest of the top tiers because of how linear MK's approach options are + again vulnerability to Flame Choke, but you're literally going to die if you get hit by a Dash Attack against a high level one.
High Tier:
Rationale: Luigi's slow air speed means he really can't ultra zone you out if you can reliably powershield fireballs. That and the fact that a Luigi who is forced to recover with down or side b is immediately dead.
Notes: The Wario matchup is kind of playable if the opponent isn't patient, but Ganondorf hard loses to good Wario's (gets camped out, cannot approach at all).
Mid Tier:
Rationale: It's incredibly easy for Olimar to wall out Ganondorf, but if you have on point powershields and yomi Ganondorf has the best punish game in the game on Olimar. If an Olimar doesn't tech a Flame Choke they can die to a Down Smash as early as 60%. Stomping their recovery is certainly the most showy, but in a more practical sense Olimar's recovery is hard countered by tipman. (knock them off stage--> hold ledge --> interrupt their up b with tipman --> repeat until tipman kills off the side). As an added note, ftilt/jab/dash attack beat out every Pikmin throw with the exception of Purple Fsmash, against which they clank. Autocanceled bair/nair and dash attack are usually the best way to knock Pikmin off of you.
Low Tier:
Notes: I'm friends with a Jigglypuff player that is powerranked in my region, and we both agree that Ganondorf hard loses to Jigglypuff. Ganondorf's recovery/fall speed/lack of combo breaker make him one of and quite possibly the easiest characters in the game for Jigglypuff to wall of pain gimp. Sure he only needs 5-6 hits to kill Jigglypuff, but Jigglypuff only needs one fair to kill Ganondorf.