I spent a few moments thinking about this boss, and I feel there's a significant discrepency between how people perceive the difficulty of this boss, and how easy it is to beat it.
AFAIK (I haven't checked any FF3/FF6A Walkthroughs as of late), but they always propose getting Phoenix for learning Life3 and/or using Rhinox's Rage and kill off a character... this is assuming you don't go through the easy route of not using X-Zone on the Soul Savers.
The normal easy route is simply learning Break and petrifying your own guys (use Vanish if needed)... then Remedy the petrified character. Petrification is treated as death, so Wrexsoul comes back and you can beat up on him w/o suffering from the required healing you'd normally have to do after reviving a guy.
That "Zinger" possession attack would be awesome an attack to be used by the Ghost characters (and maybe Gogo/Umaro?) for the coolness factor. I think if the attack were to be reworked (in a hack), it would be really awesome. Think of it being Relm's Control, only better. You (or the enemy) would use said command and possess a target (won't work against bosses though...). The character is then in a "hidden status" and the next command would be able to use some of the target's abilities (it could be a special command that executes one of the battle commands of the enemy and deal it to itself instead) in addition to their own magic.
When the enemies use it on you (monsters other than Wrexsoul should be able to use it, like the Soul Savers), they should only be able to cast magic on you... this would make for a more interesting battle. In addition, the Soul Savers should be able to heal their MPs in combat by using a Tincture/Ether/X-Ether on the possessed target (their MP drain attack sucks ass), but this also heals their target's MP as well (just to make it interesting).
When the target is in some death status (no HP, petrification, and maybe zombie status, but I don't recall if enemies can successfully inflict that status on their own and if it worked, do they die?), the target dies and normal status is restored to the character.
Thoughts? (I'm not doing this hack, but I like the concept around it, and you can use the idea if you wish).