If someone wishes to go head to head with Mormons (which I seriously don't recommend) I suggest going straight for the jugular— the priesthood order of Melchizedek; because it's the Achilles' heel of Mormonism's entire hierarchical structure.
According to the letter to Hebrews, the Melchizedekian order is a high-priest's post; and very exclusive.
1• Melchizedekian priests do not obtain their positions by succession.
2• Melchizedekian priests are personally hand-picked by God; not by man.
3• Melchizedekian priests must be immortal.
4• Melchizedekian priests must be childless.
5• Melchizedekian priests have no genealogy.
6• There can be only one Melchizedekian priest at a time.
7• Jesus is the man currently occupying the post; and since he rose from the dead immortal, he will never be replaced.
8• The Melchizedekian priesthood began with its post on earth. But when the covenant that Yhvh's people agreed upon with God as per Exodus, Leviticus, Number, and Deuteronomy established Aaron as the high priest, Mel's post was moved to heaven; viz: no man on earth can officiate in the priesthood of Melchizedek; not even Jesus; were he here.
9• No human being under God outranks a Melchizedekian priest; not even an actual Old Testament prophet.
If Mormons challenge you to produce textual evidence to substantiate those nine points: don't do it. Instead tell them that if they want textual evidence then they will just have to read the letter to Hebrews themselves because you're not telling.
The reason I recommend that stance is because Mormon men are supposed to be well-versed so that you shouldn't have to produce textual evidence. Don't let them talk you out of this by citing rules of academic discussion and so forth. You don't have to win the discussion; all you have to do is know what you're talking about; and he that's biblically ignorant; let him be ignorant still.
If the Mormons with whom you are conversing attempt to divert you, or refute you with "revelation" or in any way bee-ess their way out of those nine points with clever LDS sophistry; it's time to come to a full stop— politely thank them for their time, and bid them have a nice day.
Q: Does Mormonism's order of Melchizedek have to be biblical? Why can't a church employ the name for their proprietary order of priests; sort of like the Mason-sponsored community of Job's Daughters International?
A: Because it's fraud. Maybe Mormonism's brand of morality doesn't see it that way; but my brand sure does. Christ's high-priest priesthood is not a trifling matter; it is crucial to humanity's association with God and when Mormon men take that title to themselves, they are nothing less than identity thieves and usurping someone else's authority as their own. I can't stop them of course, but neither can I condone their conduct.
FYI: The order of Aaron is also a high-priest priesthood; so even that order is limited to one man at a time; viz: both of Mormonism's priesthoods, even were they valid, are way, way over-staffed.
The Kingdom Of The Cults
by Walter Martin