Harley has some pretty sweet zoning. After I get a knockdown from Ex cupcakes I like to charge up the Pop Pop. (fully charged pop pop moves very slow across the screen and becomes unblockable) Don't do this against opponents with teleports because the cooldown is very bad. But if the other opponent respects your charge and lets you shoot. Then it's the perfect time to use her trait. I noticed I almost always get Ivys flower which is the health boost. Don't know why
Also theres a chance the pop pop will be a dud and Harley will be like negative 100,000
theres probably like a 1 out of 10 chance of that happening though.