Macro? But really just key locked to use skill.

I read that macros that use skill on timer/repeat are not allowed.
Same with matchstick locked key to constantly use skill.
Reason is "unfair advantage" over normally playing users who aren't able to do so normally.

What about if i bind my molten shell to CTRL and since my left hand rests on it i can have it pressed all the time.
Since it's not something others can't do normally is it allowed? How 8s it different than physically locking a key?

As long as you are 'pressing' the key it's fine (if I'm not mistaken the only macro which is "officially" allowed is log-out one).

Alternatively assign molten shell (or any other Guard skill) to left mouse button, so you will use it whenever you start moving (respecting CD of course).

I've seen some threads that say locking the key is treated the same as using macro auto click.
But as i said i am simply holding the key pressed.

For left mouse i am using withered step for move speed and elusive buff.

Yes, locking the key without pressing it is also against ToS, but if you are pressing it, it is allowed.

As for other types of macros that are allowed, ones that press a different key are fine so long as they still only execute one server-side action and always execute the same action on the same key and do not cycle through different actions or select one randomly etc..

E.g. some people have their left mouse button bound to their space bar instead to avoid RSI.