maybe add gomu gomu no rocket where you can latch either onto the enemy or the ground and fling off of it

haki gimick

When i was making a luffy mod a found a lot of resources for moves, they mainly come from the One piece Wiki on the Gomu Gomu no Mi.

Do gum gum bell as his standard grab

Conq haki

here are some ideas I think might help, sorry if the amount is overwhelming, but I spend a lot of time thinking about making luffy movesets without having the actual modding skills to do so.

special stuff
1. balloon as a special block or potential alternative to the current haki for burst
2. using jet pistol. I think an easy way to do this would be to have jet pistol replace the current pistol move, and make the projectile pink and faster, but make it require 1-3 super depending on how you want to balance it
3. giant pistol or giant whip, just a punch or kick where the hand or foot is about Luffy's size or a little larger, and have this also require 1-3 super.
4. gear 4 as an attack, coding a transformation is probably difficult but I think making an attack where luffy goes gear four, uses king kong gun(giant haki coated fist) or black mamba(two fists that each change direction multiple times while in air), then leaves gear 4 all in one attack as opposed to making a whole transformation with different attacks or anything might be better. I think it might work if the attacks use up super and have bad startup but have big hitboxes and do lots of damage could pay off

basic "melee" stuff
1.axe(just rise the foot up then have it stomp down, probably more startup but can hit foes lying down)
2. stamp or whip(in a 2d game they're basically the same bu look different, whip is a curving kick, and stamp is basically gum gum pistol but with his foot)
3.spear or javelin(I don't remember the name for sure but it's where he puts his feet together while in the air and kicks down with them)

If you've read this far, thanks for reading this and I hope it helped!

gum gum firework

gum gum helicopter for sure

armament haki as a buff that u give yourself via a move

and observation haki as a dodge move

gear 5: throws lightning, gomu gomu no Giant must be epic. and The bajrang Gun, crazy gatling like this https://youtu.be/L0BqwTICxD8?t=37

gear 4th: you can have the snakeman and the bouncyman, have special attacks king cobra on snakeman and king kong gun on bouncyman.

Gear 3th: can have giant pistol, elephant gun, grizzly magnum, red roc

gear 2nd: jet pistol, jet bazooka, jet gatling, jet missile, red hawk

Luffy base: can be bazooka, gatling, pistol, rocket, haoushoku haki, kenbushoku haki and busoushoku haki, all transformations can be the special attack.

I hope I helped, I don't know English, I used Google Translate, but I really like One Piece and I already admire you for having the willingness and knowledge to do this