Ok, time to finally get this out here:
Nominating Liepard for
B-/C+ rank
Ok, so everybody knows that SwagPlay is now illegal thanks to it being banned in OU. While this may have hit Liepard, you shouldn't discount it as a solid support threat. The bulk leaves a lot to be desired and the typing may not be the best in the world, but Liepard has a fair few things going for it. I'll list those now:
Ability: When it comes to support Pokemon, there are a ton that would just beg to have Prankster. Liepard has this. Priority on all status category moves is really cool. Without Prankster, it would be hard to justify the use of Liepard over a lot of other support Pokemon in the tier, so big plus here.
Movepool: A lot of Pokemon can suffer from not having the movepool to support their playstyle. However, Liepard has everything it needs to support its playstyle. Thanks to Prankster, Liepard gets priority on moves such as Encore, Taunt, Thunder Wave, Rain Dance, Sunny Day, and Yawn. And let's not forget Liepard has a solid pool of Dark-type STAB moves to pick from. Foul Play, Sucker Punch, Pursuit, and the newly buffed Knock Off are all available to Liepard to use. All four moves have their uses and can allow Liepard to check even more threats depending on the Dark STAB it carries. But it doesn't end there. Liepard has U-turn as well to build momentum. So, unlike many support Pokemon, it won't kill your momentum to send Liepard in to prevent something from setting up. Encore + U-turn WILL get a setup opportunity when you play it correctly.
Free Switch-ins: While Liepard has a hard time finding a time to come in itself, it won't be giving up many free switch-ins either thanks to its wide pool of support and Dark-type STAB moves to choose from. Obviously, there's going to be some things that get a free switch-in depending on what you run, but if you don't want something in particular to have that free switch-in, there's probably a move to help with that in Liepard's movepool
Now, with pros, there will be cons, so I'll list some of those as well:
Typing: Dark is not a very good defensive typing. Liepard may not provide a ton of free switch-ins, but it's also going to have a hard time with many of the top wallbreakers in the tier, especially special-based ones such as Moltres since they won't mind Foul Play so much. Fighting-types in general will give Liepard a really tough time since it rarely runs any offensive moves outside of U-turn + Dark STAB, though you can use Thunder Wave to alleviate this somewhat as most Fighting-types loathe paralysis.
Bulk: A lackluster defensive typing combined with lackluster bulk. Yeah, Liepard won't be taking a lot of hits, and it will go down to most super effective hits. This is quite unfortunate and a stark contrast from other Prankster Pokemon in RU, such as Meowstic-M and Whimsicott, both of which have some bulk to work with. When defensive shit like Aromatisse and Cresselia (with a CM boost) can OHKO Liepard's typicaly max HP/max Speed spread with Moonblast, you know the bulk is p. bad.
4MSS: Liepard has a good range of support moves and STAB options. Problem? You can't use them all in the same set. Liepard generally needs a STAB move and greatly prefers U-turn to build momentum and provide easier switch-ins for teammates. This leaves you with two moveslots that you can use for any number of moves. (Encore, T-Wave, Taunt, Rain Dance, Yawn, Sunny Day) While two of these moves are specific to certain archetypes, that's four moves for two slots. As for STAB moves, there's that problem as well. (Knock Off, Sucker Punch, Foul Play, and maybe even Pursuit) That's at least three moves Liepard wants to run, but it will usually only have room for one. Although Liepard can handle quite a few threats, it will be difficult to do so with one set.
TL;DR Liepard is a mixed bag with quite a few pros, and some glaring cons. It's usable for sure, but its cons weigh it down a fair bit. It can do well, but you'll need to support it properly. This makes it fit into
B-/C+ imo. Discussion, commence!