Hey GH! I'm guessing you're quite busy with setting up and all that but once you do, there's a million things you could do to improve SK. Few of them would require little effort however, so I figured I'd compile a list of things that are most probably really simple to fix that have been a problem for the game for a long time. These are not bugs, just small balance and mechanic stuff that's pretty much universally agreed on fixes.

1. Shard Bomb invincitinks are super buggy and really cripple the weapons. Meanwhile, it's at far less damage than most powerful weapons. Removing them will make for a more enjoyable experience while not in any way risking making a broken weapon, at least if we compare to the likes of Blitz Needle and Iron Slug.
2. Acheron's combo damage is too high. While it's understandable that the charge is stronger than its peers' since it has no status, it's questionable that Acheron has a higher combo damage when the Brandishes don't get status on their combo.
3. Sudaruska's stun on combo was removed back when stun was super buggy. It's not super buggy anymore, but Sudaruska never got its stun on combo back.
4. Divine Cloak doesn't have a Fiend damage bonus while Divine Hood does. Either give both a medium bonus, or give both a low bonus. I'd go with the former to keep it more in line with gear like Dragon Scale and Radiant Silvermail.
5. Blackhawk (specifically; not Sentenza) has ridiculous bullet mechanics where the bullet is fired from within your body and thus gets a lower range and it can break Rocket Puppy missiles.
6. Overcharged Mixmaster has an incredibly obnoxious shaking effect. Please at least give us the option to disable it (or camera shaking in general).
7. Wild Hunting Blade and Cold Iron Vanquisher are slower than Dread Venom Striker and Leviathan Blade respectively for seemingly no reason at all.
8. Seraphynx's damage vs fiend and undead ultimate is significantly worse than the defence reduction alternative, as the defence reduction will result in virtually the same damage output against fiends and undead. Increase the damage bonus greatly, maybe even to 2x the regular damage.

Let's also talk about more controversial changes and/or things that would be harder to implement:

1. Old Radiant Sunshards were amazing and no one saw a proper reason to remove them. In fact, by removing the old mechanics, it's estimated that the bear population of SK fell by 40%. Please re-implement them. That said, the new shard bombs are cool too, so let them coexist. I'd like to point out that (part of) the reasoning was that they weren't enough like bombs (even though they perfectly mimicked a common bomb mechanic from old school games). A few years later, Tortofists were introduced and they aren't very much like guns, even if they're really cool and I like them.
2. Iron Slug's knockback is really weird; enemies are knocked in the direction that's backwards to them, so if you shoot a Zombie west of you and it's facing up, it will be knocked south instead of further west. This may be a simple oversight but also harder to fix, I wouldn't know.
3. Mad Bomber was pretty much obsoleted when Chaos was buffed. There's a lot of ways to approach this. A simple fix would be to increase the bonuses to High on both pieces; another would be to nerf Chaos somehow. This has been discussed a whole lot and many good ideas have been mentioned.
4. Cautery Sword is more or less obsoleted even at 3* since its Shadow variant will presumably outdamage it against Slimes. One fix for this could be to give it split Elemental/Shadow damage, making it very useful for Royal Jelly Palace.
5. There's some pretty odd balance with Autoguns. More specifically, Grim Repeater has less damage than Blitz Needle while also having knockback, which is not beneficial to its damage output.
6. Heavy Deconstructor is pretty bad right now. One way to make it more interesting would be to make it elemental, giving bombers a new option for a solid damage output.
7. Winmillion is really cool! Give it a 5* version and maybe split normal/piercing damage to make it a solid alternative to toothpicks.
8. Seraphynx's Angelic Aura works quite poorly: team members can break it (or maybe this was fixed), the shield regeneration ultimate isn't too helpful (make it instantly put your shield at 100% perhaps?), and the charge time reduction ultimate is capped and doesn't change anything if you're already at Max charge time reduction.
9. Seraphynx's Violent Heart Attack explosions and Maskeraith's Haunting Haze and explode-y cloak do virtually no damage. Let's make them virtually do damage.
10. Defence trinkets are way too weak to be even situationally worthwhile. Similarly, resistance trinkets are quite weak and could definitely stand a buff.
11. Volcanic Pepperbox's inverted knockback was really fun. A lot of us would enjoy seeing it reimplemented, although it might be a questionable move.