Reverse bair while landing -> dsmash/Dolphin Slash. Also works with Roy.
Also if the above gfy didn't give you enough ideas, in general, moving forward with a reverse bair such that it knocks them in the same direction as you sets up for a lot of things, often up airs, sometimes single hit nairs (Both usually while reaching the apex of a jump, though whenever I'm getting something out of it, I find I'm doing the bair a little earlier than Armada does it in that gfy, and in a motion maintaining momentum).
Reverse dair edgeguards (idk if you want to count these as "reverse aerials"), if you know how to move to position them, aside from obviously having good uses from a ledgehop at times, can be used to aggressively edgeguard many floaties, Falcons, or even spacies charging Fire Fox/Bird.
Reverse fair, if they DI to avoid the dair, often leads to descending bair tipper. If done low to the ground, may combo into all of the things fair normally comboes into.
Any situation where you can move towards the opponent slightly and have them overlap Marth's center during the active frames means an opportunity for a reverse aerial. Aside from often being DI traps, this legitimately can be a way to mitigate overshooting the effects of overshooting the opponent while facing them (and reverse hitting them so they go the opposite direction you are), allows you to hit later in the hitbox in a controllable way, and minimize the distance between you and your opponent during a combo, so reverse hits are actually a lot more useful than just swag.
Play around with em'.