Comparison
First, look at similar items. For example, if you want a permanent item that lets someone fly, look at jump jets, which only boosts a character into …
First, look at similar items. For example, if you want a permanent item that lets someone fly, look at jump jets, which only boosts a character into the air for 1 action and thus can't be used to gain a huge advantage in combat, and jetpacks, which can. This will give you an idea of the right level range and the specifics and limitations of existing items. You might be able to just adjust one of those to get what you want.
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