Regarding the Falcon/Jiggs MU
Keep this in the back of your mind while you read this, or any other post regarding the MU: it's very unexplored, and we don't have enough information on it to truly come to a conclusion.
If Falcon is sent off stage and the Puff pursues him, he's more than likely to suffer a KO. Even at low percents, Falcon is in danger of being KOed via gimp. For this reason, Falcon doesn't particularly want to go off stage as much, keeping his overall game very grounded. Through the combination of a poor recovery, Puffs long lasting hitboxes, and her multiple jumps, Falcon gets messed up while off stage. The disadvantage state for Puff can quickly turn into Falcon being KOed.
What's more is her crouch shuts down his grab game, which generally speaking, is the starting point for several of his combos. In the case where Falcon manage to land a grab, due the the floaty/light nature of Puff's character combos tend to be shortened and rendered as ineffective much earlier than they would on the rest of the cast.
Most of what makes Falcon great (e.g. grab game, offstage game, combo game, etc.) is much less prominent in this MU.
On the other hand, Puff dies extremely early to a plethora of Falcon's moves, including but not limited to Knee, Bair, Dair, Dsmash, Fsmash, Raptor Boost, and Falcon Kick. The catch is, Falcon has very few set-ups into these moves meaning Puff will only die should the Falcon make a read, the Puff make a mistake, or some combination thereof. Of course, the threat still stands.
If the Puff isn't able to secure a gimp, it becomes more of an uphill battle for her (though I wouldn't necessarily call it disadvantageous). Her hits do less damage in comparison, and she doesn't have many combos to quickly rack up damage. At higher percents, it quickly evolves into a game of
catch me if you can with the Falcon charging at the Puff, and the Puff abusing her aerial mobility and airdodges.
The MU could be anywhere from 40:60 to 60:40. L̶e̶t̶'̶s̶ ̶j̶u̶s̶t̶ ̶c̶a̶l̶l̶ ̶i̶t̶ ̶6̶0̶:̶6̶0̶. Until more people give Puff a chance and explore the MU, it's going to remain a mystery.