Here's a fun little patch I made today which makes the health and ammo counts on the HUD animate when they change.
So, when you pick up 4 health, the health counter will slowly increase by 4 over the course of 16 frames at 1ammo/4frames, for example.
Note that this doesn't affect gameplay, only the HUD display, so behind the scenes all of the health and ammo counts get updated instantly still.

By default, the ammo counts update by 1 ammo every 4 frames, while the health counter dynamically changes it's increment speeds based on how desynchronized it is with Samus' actual health. This can be edited by changing the asm file.
Uses some freespace in $80. Tested with asar, should work with xkas as well.

A fun side effect is that when loading into the game, all of your equipment counts up from zero during the loading animation.
Uncomment the code at the end of the file to revert this change, but I think it looks cool, looks like your HUD is booting up or something.

Please give credit if you use it in your hack, and be sure to let me know if you have any issues with it. Thanks and happy hacking :)

UPDATE v2 March 30, 2023: Gave the health counter some special coding to scale it's animation speed based on how far behind Samus' actual health value is. It is much more responsive now.
UPDATE v3 April 1, 2023: Sorry for update spam, but this should be the last update. I kinda went back and forth on whether the ammo counters should use the updated health counter logic (which is a tiny bit more complex) for performance reasons, but in the end I decided it is better. In an isolated test I didn't experience any lag frames while all four counters were increasing using this logic, so it should be fine.

ALSO, please see forum post for some optional bonus features. I updated that section today as well.