What do you want to achieve?
For the breathing/idle default animation to not interfere with my animations
What is the issue?
When the player moves/stands still, default animations make the arms move along with them and it gets held in weird ways.
How can I disable/overwrite it while the tool is held?
this is probably due to your animation having the same priority as roblox does, either increase your animations priority or make a custom animate script to not have a tool hold animation
Personally, I believe weapons should be welded to the arm that holds the weapon, instead of HumanoidRootPart (it looks like you’ve welded it to the HumanoidRootPart).
Doing so prevents issues like these, because weapons will always follow the arm that’s holding it.
The animations priority is set to Action
How can I do this? Instead of setting Part0 to the HRP, an arm?
I tested this out and it doesn’t fix anything, if you attach it to an arm, the gun goes inside that arm and if it’s attached to the Torso, the gun isn’t animated.
You will need to re-make the animations with it welded to the arm instead of the HRP.