So here is what I'm thinking as regards to magnet release.
First no third kazakage jutsu!!
That suppose a magneto level of mastery over all magnetic forces including but not limited to the magnetic poles of the earth and any known or unknown magnetic substance...you could literally destroy the world of slo with this level of jutsu. Magneto never did it but if he wanted he could create micro holes in the earths magnetic feald and burn people alive with solar radiation. The iron sand is actually a week jutsu compared to what you could do with control of this abuilitys.
So I suggest magnet release be more like Jiga'a
Magnetic forces with out the need for stoping- as long as you have chakra your good!!
This still gives you the abuility to pull and repel magnetic object as well as form them in to useful weapons and defense.
To that extent wind and earth is not conducive to making the magnetic fluid but I like the idea of it so maybe you could draw it out of a nearby streem or water source and carry it with you. The other way is using the water and mineral in your body to make it. But this should be a forbidden jutsu and cause major damage to the user.
However when real ferrofluid is exposed to intense magnetic fealds the magnetic particles clomp together and can not be reintroduced in to liquid state. This should be the same for magnetic release effect on the flued. Meaning after you use up the fluid you have to replace it. If you solidify the liquid in to a solid weapon or armer then you can't make it liquid again.
This fluid would be made from the resorses iron and a fluid. Water would be the simplest form but you could make it out of liquid poison as well. Mostly venom basted poisons.
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