Well, I may not be pure on the matchup with the lack of recent great experience, but I can probably think and think based on some experiences. Everything that's between the lines is in my document that will hold all of Pit's matchups.
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Matchup: Kirby
Intro: Pit always had a bit of a problem against smaller targets since it's hard to hit them or to shoot them with arrows. That's where Kirby is going to give Pit problems.
Range/Priority
Okay, Kirby and Pit both have similar ranges, but Kirby's B-air is probably more threatening to Pit, being able to destroy arrows when timed right, and to gimp Pit, too. F-air is also threatening to Pit with it's multiple reaching hits. Pit can't spot dodge or air dodge the full move, for the 3rd hit will get him. For Pit, F-air is probably his best choice, since it is disjointed, and is perhaps Pit's longest ranged move, along with his laggy F-tilt. Pit's Angel ring can be outprioritized by a Kirby Fsmash. Kirby seems to do slightly better here.
Power and Weight:
On the Power and Weight side, Pit weighs more obviously, but Kirby has the better power. This would probably be in Kirby's favor since his Power is just rough, especially the Fsmash and Hammer. Kirby's light weight, however, does help Pit KO decently, for Pit alone, has poor KO power. His Fsmash and Sweetspotted B-air are Pit's best KO moves, which still have some poor KO power. So again, Kirby would win this section on Power.
Camping:
For Camping, this is sort of tricky. Pit has his famous arrows, but Kirby is a small target, hard to hit. Plus Kirby can make attempts to B-air the arrows too. Pit, however, succeeds Camping just for having a long-ranged projectile, even though Kirby is hard to hit, and Kirby will have to approach eventually.... Well, unless he does have Pit's arrows, but even if he does, Pit still has reflectors.
For Pit's ledgecamp, it really is a tough one compared to many others, being able to arrow away even from the ledge, but again, Kirby is a small target.
Basic things/other:
Well, Kirby still has his F-throw to U-air that works on Pit, and for Pit, though he originally had his F-throw to stutterstep Fsmash, which could do 29-30% damage max, starting from 0, won't work on Kirby, for he can DI away from it. Pit can try to mix up his disjointed F-airs with arrows, making attempts to space and pressure a bit, though, again, hard to hit Kirby. Nothing much to say here.
Edgeguarding/Gimping:
For Gimping, Kirby to Pit, Kirby's B-air alone is a threatening factor to a recovering Pit. F-air works too, really hard to dodge with its multiple attacks. For Pit's Gliding, a B-air can do just fine since the glide attack is hard to angle and time. As for Pit's B-air, all you have to do is hit him, and he can't use it again. Pit could retaliate with Shooting arrows at he recovers, or an F-air too, though kinda hard with Kirby's B-air in the way.
Now, if Kirby does have Pit's arrows, then it just helps him even more. T_T
For Gimping, Pit to Kirby, Pit does have potential to do so, but it is hard since again, Kirby is small and hard to hit. Most Kirbys do like to recover from a high elevation than a lower elevation. He can use Side-B to help recover slightly and attack at the same time, constant F-airs to give pressure, and with 5 mid-air jumps, it's difficult for Pit to get him. He can easily go towards Pit's arrowing blind spots, where the arrows can't curve in to hit him.
Pit's Angel Ring can help if he can knock Kirby back a bit, hoping that he isn't higher than Pit elevation-wise.
As for Kirby's Up-B, Pit can mirror shield it to kill him. Even the tip of the final cutter is a mirror shielding target for Pit to use to his advantage. Getting a Kirby to use Up-B is sort of hard with the multiple jumps and all, but if he is capable if limiting Kirby or getting him to use Up-B, that mirror shielding chance is what Pit needs.
Pit Kirby: Kirby with Arrows (Kirby-exclusive)
A Pit would think in his mind, "Let me go!"
For Kirby, he should try getting those arrows whenever that opportunity comes. This way, the Kirby has his own means of camping, and a better chance at gimping Pit better. You can control the arrows just like Pit can.
Be warned, though. By having Pit's arrows, do watch out for Pit's multi-hit attacks, like his infinite Jab, N-air, U-air, and Angel Ring. Each hit is a chance of you losing those powers. So a Pit that may spam these moves may be trying to forcefully take away the arrow powers that Kirby obtained.
Special Note: For Kirby, when under the stage, while trying to get back up, watch out for Pit's D-tilt, which does have potential to spike. The hitbox of the spike is where u r really close to Pit, as in touching him around his feet when Pit executes the move. The spike is sort of strong, actually, not Ganon-Strong, but probably Ike strong. You pretty much won't survive at around 40% and the D-tilt does 11% damage max.
This may not be likely, but it helps to have the knowledge.
I find the overall matchup to be around 55:45 Kirby's advantage, could slightly end up being 50:50 eventually.
It's Kirby's power with some priority, size, and good capability of gimping Pit while Pit has hard times hitting him that's really the problem. Even though Pit does have the disjointed F-air and ability to camp, he is limited, trying to hit Kirby, and has recovering difficulties.
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Now, this is my own data all from wifi , experience, knowledge, and BEFORE u bash wifi and all, be glad that I have provided a some info, and those tourneyrats think they are all that, when I could be as good as them at discussions and such. (Sorry if that sounded kinda harsh, but it annoys me when ppl don't take my info because it's associated with wifi)
Some info is better than none, right?
But anyways, I do have a request for the Kirbys. I would like to know the name of any good Kirby with some good Pit experience to help make a summary in the Pit v Kirby matchup, from the Kirby's "Point-of-view." The more the merrier. This reason is so I can continue supporting the Pit players with an attempted complete summary on every matchup.
What u read that's between the lines are all in the document that will hold all Pit matchups in it.
So I would appreciate if you guys can help me out with that part.
BTW, another thing. We may need to know Stage CPs/Bans due to the outdated CP/Ban list that we have.
The only thing about stages that I know are the following:
Yoshi's Island: Pit's worst neutral by default, due to it limiting Pit's recovery really well, (Can't glide under the stage) allowing u to gimp him easier. The Shy guys also block the arrows too, so camping may be a bit harder on Pit's part. You can CP this against Pit if you wish.
Lylat: I actually dont know about this. It affects Kirby's recovery, but most Kirbys prefer to recover from a high elevation. Pit can fly under the stage at will, and his projectile can be curved, so the tilting stage really cant ruin the arrows much. So idk if this could be a CP against Kirby or not.
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So again, I hope the info helps.