A monk's unarmed attacks are treated as magical weapons, so that's not a problem. Whether Quivering Palm is considered a magical effect is up to the DM. Personally, I would use antimagic field as a guideline--anything that gets shut down by AF is considered magical; anything that doesn't, isn't.I'm not sure that QP works on the Tarrasque: it's immune to damage from non-magical weapons. OTOH the text for QP doesn't say that you actually have to cause damage for QP to work.
And does the Tarrasque have Advantage on the save too? Is QP / Ki considered a magical effect?
A monk's unarmed attacks are treated as magical weapons, so that's not a problem.
Whether Quivering Palm is considered a magical effect is up to the DM. Personally, I would use antimagic field as a guideline--anything that gets shut down by AF is considered magical; anything that doesn't, isn't.
I've got the PHB in front of me and can't spot where it says this.
I've got the PHB in front of me and can't spot where it says this.
Level 6, Ki Empowered Strikes.
The maximum DC for the save is 18 unless I am missing something. 8 base, 5 Proficiency, 5 Stat (20 Max) = 18. With advantage the Tarrasque is only going to fail that save 12% of the time, not 16%. The odds of him failing that save 4 times in a row, and thus dying from it (in a minimum of 8 rounds) is less than 1%.
OTOH I can now answer this: the PHB says on p76 that Ki effects are magic, so the Tarrasque would get Advantage. It also means that monks inside an antimagic field are no longer the killers they once were.
So, tarrasque get advantage as well. Nice.
Though, I'm not really sure about ki being necessarily magical. You're right, it says so right there in the PHB, and it would definitely hold with respect to certain features (elemental monk spells, for instance, and others), but total adherence to "ki is magical" would have numerous other effects. Would a monk in an antimagic field lose his immunity to disease and poison? How about rerolling saves as per Diamond Soul or stunning an opponent with a melee attack, or pushing him away with Open Hand technique?