I MT'd naxx in like... Sunwell/T6 gear and random quest/heroic blues. I think MAYBE around 28-30k HP. Imo if you're def capped and know how to use cooldowns well you'll be fine. The only hard fights I'd imagine would be patchwerk, thaddius, and saphiron. And if you can survive patchwerk you can probably survive the other 2.
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