Latest version of cairn wraith is below - I need to sleep now
G'night!
Hmm, the
Life Drain is completely different from the standard version so should be renamed.
I'd suggest just recycling the
Death Grip and/or
Soul Drain of the
Cairn Wight (Undead Stone Giant) rather than reinventing the wheel.
Also, I wouldn't have it do 2 levels of exhaustion per hit AND give it two attacks with Multiattack. With its Legendary Action option the Wraith can make three exhaustion-inflicting attacks per round so can kill a PC in a round if they're unlucky.
Contrariwise, at most the
Cairn Wight (Undead Stone Giant) can only do four levels of exhaustion per round, two with its standard Action and two as a Legendary Action, and the target has to fail two DC 10 Constitution saves for that to happen (since it must miss its DC 15 CON save by 5 or more).
Now that I think of it, that DC seems extraordinarily low for a Challenge 16 creature. The recommended DC for a CR 16 creature is 18 after all.
While I did deliberately gimp the DC by making it CHA-based instead of CON-based like a standard Wight, maybe we should go back to the default and make it CON-based for the Cairn Wight, which'd give its
Death Grip and
Soul Drain DC 19 (so the target would have to miss a DC 14 to get two levels of exhaustion, which is pretty easy for a Challenge-appropriate PC).
Should I update the
Cairn Wight (Undead Stone Giant) with DC 19 for its life sapping special attacks?
Oh, and the Cairn Wraith's "
Life Drain" should use base 8 for its saves, not base 10, which'd make the DC 16 rather than 18.
The easy fix is to increase the CON a bit and knock off a few HD.
Both Wraiths and Wights have CON 16 (+3) in 5E so I think you'd be justified in giving a Cairn Wraith the same CON 22 (+6) as the Cairn Wight, or if you prefer to keep the DC 18 make it CON 20 (+5) like a living Stone Giant.
I lean towards CON 20 so the Cairn Wraith is a bit more ephemeral than the Cairn Wight.
Either way you'd need to knock off a few Hit Dice assuming we're aiming for the HP to be in the same ballpark of 209.