This kind of stuff might be a toggleable option for people when creating due to the complication, but this could be a great feature for advanced creators and more of a late-night brainstorm- I will simplify things at the end if you wish to skip there.

Let's say you want special animations to play when you equip, left/right click with certain items- how would you go about this?

I propose an idea that might make it simpler to set up; by adding animations that play when- you equip, hold, left click/hold, right click/hold, drop and attack with with an item, you could bind them to items (i.e. iron_sword), specific tags perhaps non-vanilla ones too (i.e tconstruct:sword), or even things with a certain phrase in the name (i.e. "sword" or "pickaxe"), and of course you could specify if any hand is needed (i.e. is in JUST left, JUST right, EITHER)- this would obviously allow you to bind multiple tags to one animation because one tag won't cut it for some animations; and animations bound to the same tags could play at random each time you meet the "requirements" to play the animation.

To add on with "requirements", you could link things like player hunger, health, and maybe add this option to set up requirements to play existing animations like idle, walk, run, etc. This would allow people to set up extra animations if they so desire. And if requirements are met, they could play on the dot/constantly in a loop/just once, or play at random (i.e. extra idle animations like looking around that'll play at random when you stand still for a set amount of time) though I'll get in depth later on.

Some examples for left clicks are- either no weapon/item in your left hand could allow you to have a custom punch/breaking animation(s), having a sword would let you play custom swinging animations, pickaxes for pickaxe swinging and breaking separated, and can be the same for axes, shovels and anything else.

For right clicking, it could be for a custom block animation for shields, custom bow draw back (with possible bow in animation maker for reference), opening a chest (idling in a chest inventory) and closing it.

What do I mean by more? I'll get sort of in-depth here.

Taking into account you could have animations play with "specifications" you set up, you could mix animations together.

For example, you could have animations change dependant on how much health you're on (i.e. Idle pose could change to look progressively more injured), hunger could change all animations you specify or maybe add the occasional animation to play over for example- an idle where you look down and hold your belly, a kind of animation stating "I'm hungry". You could also bind things like drowning, taking damage, burning, withering, freezing, any potion effect (including non-vanilla ones via specific names like "tconstruct:insatiable" so advanced creators can get creative)

Adding onto my previous suggestion (#79) animation blends could be taken into account for all said above (and below). For example, certain animation blends could just play with one, or multiple requirements being met. Going back to attacking or holding items like a sword- you could make things like different attacks for different speeds in walking and running (i.e. a static slash animation(s) for idling, special animations for walking, running, jumping and/or falling, including a mix of adding walking/running and jumping).

And to make it easier to add onto animations through requirements (like holding a sword) you could have a "preview animation" of choice, so you can animate the arm in perfect sync with the run animation, so then in-game when you test it the run animation will play normally, but when you equip a sword, the base run animation will play normally, but the "run with sword" animation will play on a higher priority (if set).

An idle slash with a sword would be a normal slash (or whatever the play decides to animate) and if you have a variant for falling, you could do a downwards slash (and another animation for falling in a certain direction if you want to).

Some examples with animation blends needing requirements- normal running/ground-based locomotion would need you to be- on the ground, hunger over 5 bars, health over 5 hearts.

To simplify, there can be specific requirements for animations/custom poses based on left or right clicking, health or hunger amount (either over/under a value/within a range), walking and/or running, starting to run/stopping a run jumping, falling down, with a specific item in the left, right or both hands, crouching, with a specific potion effect, wearing a certain item (like armour or an elytra), and so on. (And if possible, for doing certain things/triggering custom mod abilities like the grapple mod's slide, double jump and wall running enchantments, these extra types of "requirements" could be sorted by having CPM (this mod) scan for abilities of items)

Some simple requests would be to allow parts to inherit player head movement (just allowing other parts to be moved around and have a percentage of how much it moves (100% for exact movement, 50% for it to move half way, etc) And maybe the ability to possibly bind more gestures/have more keybinds.

These "requirements" can just be set up by the player (or base ones could be automatically created in the tools section to make blends/certain requirements set up easier) so as said at the start of this suggestion, this could be great for advanced users and was a late-night brainstorm, I hope any of this suggestion will give you some food for thought.