Something I haven't seen discussed elsewhere, but wanted to confirm I read the rule correctly:

Diamond Soul grants proficiency on "all saving throws". That includes death saving throws, even though they are not related to a specific ability, correct?

Similarly, the second benefit of Diamond Soul (spend ki to reroll a saving throw) does not state that it is an action, bonus action, reaction, or anything else that would be limited by being incapacitated, so my reading is that it could be used on death saving throws as well. 

If this all works RAW, then Diamond Soul is even better than I realized.

Yes, the feature applies to Death Saving Throws. They are a special type of saving throw but are a saving throw. So with Diamond Soul you would be rolling 1d20 and adding your proficiency mod, with the option to re-roll using a ki. 

Quote from Cyb3rM1nd >>

Yes, the feature applies to Death Saving Throws. They are a special type of saving throw but are a saving throw. So with Diamond Soul you would be rolling 1d20 and adding your proficiency mod, with the option to re-roll using a ki. 

 And the reroll would have to be used, correct? If so, that’s a gamble. 

Quote from eightyocho >>

Quote from Cyb3rM1nd >>

Yes, the feature applies to Death Saving Throws. They are a special type of saving throw but are a saving throw. So with Diamond Soul you would be rolling 1d20 and adding your proficiency mod, with the option to re-roll using a ki. 

 And the reroll would have to be used, correct? If so, that’s a gamble. 

 
Correct.

Not much of a gamble, because you choose to use the Ki point AFTER you have failed the first save. So the only gamble is the 5% chance of rolling a natural 1 (2 death saves).