If you use Ritual of Returning instead of Returning, you can gradually put Returning on all your S1 commanders with just a few starshine skullcaps, and then do something else with the skullcaps. That's something to consider.
The catch is that that kind of returning doesn't work until after a commander takes a hit, and that first hit might still be enough to kill him. But it appears that these navigators have A1 consistently, so you could then give each one a single air gem and have him cast Mistform, maybe... or maybe it's all just too much trouble.
Re: returning spell
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