Wish for the exact base unit type, ex. 'King of Deeper Earth' or 'King of Banefires'.
Heh -- the Wish(er) could also have wished that Aegis or Magebane out of the King's hands, first. Doesn't work too well for cursed gear, 'tho, unless the Wish(er) doesn't have the appropriate slot.
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Are we insane yet? Are we insane yet? Aiiieeeeee...
Actually by the point you're dropping a wish every turn non-unique tartarians are probably taking over most of the SC duties, so this tactic doesn't work.
Besides, with a reasonably priced gear setup on the SC blowing 100 pearls to take down a single unit isn't really a particularly good value unless you're sure you can steal it, not just kill it.