you can't really be full screen against grundy, he actually outzones you there (he gives no fucks about your horizontal gunshot)
you need to be in air shot range
green lantern should just be "bend over", you are not safe from him anywhere
you do not want to be full screen against green arrow, he wins that war all the time
you want bane full screen
nightwing is two match-ups, with escrima you want to be at full screen, with the staff you want to be outside of sweep (although his staff stance ruins harley's day but who doesn't at this point)
-Grundy- MB swamp hands can be blocked low.. Your horizontal gun shots beat him out of regular swamp hands, forcing to make poor Solomon favor the D to block position (which they tend to favor after multiple dashes anyway. Grundy is your typical grappler- and logic says.. KEEP HIM AWAY AT ALL COST (see Zangief in SF). Once Grundy gets in.. F3 works wonders on a dash happy Grundy... Don't be afraid to MB B3 if you have a trait grab happy Grundy.. When he advances- you should not be aiming to hit Grundy from the front.. You want to get over top of him and let his momentum carry him forward and attack from behind. Grundy can NOT out zone Harley. It is when Harley quits winning the zoning battle, gets bored and decides to get cute and smack Grundy that usually ends up in a dead Harley.
-Green Lantern: you are 100% safe from at range (not mindlessly however). If you zone unwisely you will eat his missiles . However, his horizontal missiles are 100% duckable and in many situations can be countered with a gunshot then safely ducked. He will not use jumping missiles unless he is eating clock on the defensive (many if not all can be avoided by backdash or walking back, or blocked high) GL is NOT banking on his jumping missile chip to beat you.. So what are his other options? Trait full screen Gatling gun? Block and counter or wait out trait... Continue..
His turbine attack thrown from ground? Gunshot eats it, Air? Cupcakes eats it.. GL is your bitch from full screen. What this also will do is frustrate him into trying to get in ASAP- air turbine ride? If you have life lead on GL and he is fullscreen.. a neutral means prepare for air turbine!!! Cupcakes eat it alive.. And GL's get VERY antsy when you are out of Lanterns Might and Sliding sweep kick to follow up range.
-Green Arrow- his green arrows are worth 1% on hit.. Trades are good. GA's tend to like the crouch fire position in a fire fight.. Once/if you have the superiority your gunshot eats his arrow start up- on ANY arrow.. Outright on green arrows, special arrows may still fly toward you- block them. This forces GA to again.. Blind rush you sloppily to get in out of frustration. Dashing, jumping or dash and slide combo's.. Use Harley's tools to send him back to his corner.
-Bane: has 3 types of armor to disagree with keeping him at full screen.. Not to mention, from full screen you can not make him properly pay for venom usage during his debuff time.. You want him outside sweep when that debuff hits because that is where the MU is won. Bane like Grundy tend to favor the D to block position, and are especially fond of their quick and long reaching low kick.. It is also very hard to exploit these two things from full screen- except for perhaps (readable or predictable) cupcakes or pop pop.
-Nightwing- out zones Harley in both forms.. His escrima stance: He ducks your gunshots, you jump his sparks- draw! You are more mobile during his escrima stance (during a fire fight)- use it to get half way and air gunshot him for his trouble: Careful of his wingding counters.
Staff stance: call him Aquaman.. Just like you should NOT try to outzone AM, you should treat staff stance the same. You rule this MU in the air and outside sweep distance.. His lack of mobility/jumping should be taken advantage of.. And Staff Nightwing is ALL about momentum.. Once he gets going he is hard to stop.. Use push block to get some space and don't let him gain momentum.