I hope you don't mind bulbapedia!
Liepard is a fairly niche Pokemon in UU or maybe extremely niche depending on your opinion. It can do a few things all of which can be discussed here. Number one is the Nasty Plot set which is not too good in my opinion and number two is the Swagger set which is also not too good in my opinion because it relies on a less than 50% chance to work usually (accuracy plus confusion chance) which is just asking for trouble.
What I would like to discuss the most is a set like this
EVs: 252 HP 252 Spe 4 Def
This set always requires Ditto support so it can copy hazards while assist will never pick Transform. The next step is to stuff your team with moves that Assist will not pick like Focus Punch and phazing moves. Thus Assist will have a 100% chance to pick the phazing move and your opponent will be priority shuffled for about 60 or so turns and die from their own hazards.
This set is really infuriating but obviously has some flaws like losing to +2 or +3 (Extremespeed and Fake Out) priority and if your opponent has no hazards then you almost certainly lose since your team can have almost no real moves to ensure Assists always works. There are probably plenty more ways to beat this strategy I am not even thinking of so you can discuss those too.
Please discuss anything you want about the competitive aspects of Liepard!