Personally, capturing the stereotypical malef dragon's interest would be really fucking bad... A mindflayer would be pretty bad too.
For our protagonist, a
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would likely be the greatest struggle to deal with.
For my protagonist, since he's weak to oral, the worst offenders (other than the obvious White Succubus) would be
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for their tongue (they'd also be rough for those weak to kissing),
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since oral is their forte,
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simply for the fact that with a touch she can tell what a guy's weakness is,
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, some of the Oni girls because they like pouring alcohol on a guy's cock before sucking it,
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because they give that electric oral...
I'd really like to see our protag getting a
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lover, just because that sets them up pretty nicely to later seduce any monster girls who are really into fighting like dragons, lizardmen, etc.