Castor:

Castor has a disjointed hitbox on his up B to protect him from spikes.
Castor dair is no longer able to whiff punish other states.

Zeniah:

Zeniah has a disjointed hitbox on her up B due to its rapid upwards movement.
Zeniah dair is no longer able to whiff punish other states.
Zeniah's dagger projectiles now are out for twice as long.
The runes on Zeniah's blades no longer have glitchy visual artifacts.

Vesper:

Vesper dair is no longer able to whiff punish other states.
Vesper's neutral B can no longer whiff punish other states. This means that you can trade with her neutral B much more easily.
Vesper up tilt now has more end lag.
Vesper's down air now can't double jump cancel until after the full swing is complete (but it can still double jump cancel on hit).

Stinky:

Stinky dair is no longer able to whiff punish other states.

Selmani:

Selmani dair is no longer able to whiff punish other states.
Selmani's side b can only be shortened late now.
Selmani's shine now has reverse scaling.

Atliss:

Atliss neutral B can no longer grab whiff punish hurtboxes.

Tycho:

Tycho's stars now have a 10 star maximum.

General Changes:

Shines can now be double jump canceled on whiff.
Shine (down b) does not buffer during short hop, but cancels it instead, allowing for multishines.
aSDI applied on hit to melee attacks in the digital direction of your control stick if hit with the same move multiple times in a row. (Automatic stardust DI)
A major performance optimization from the Rainbowcore engine to reduce CPU usage has been implemented.
Menu navigation from the combo trials dropdown to the resume pause button has been made slightly easier.
You can no longer get soft locked on the credits by menu-navigating off screen.
The credits have been slightly updated, with the Stardust community now directly thanked. The game's two developers are now credited as co-creators. (as always this entire project is developed by only two people!)
Characters can no longer enter the stage walls due to bounding box changes between states.
There are likely also various other undocumented fixes.
And lastly,
A stowaway has been rumored to be lurking...