I am currently playing a Rogue who is the party's 'healer'.
I put that in quotes because he's taken a background of Back Alley Doctor, meaning he has the Risky Surgery feat which says:
Your surgery can bring a patient back from the brink of death, but might push them over the edge. When you Treat Wounds, you can deal 1d8 slashing damage to your patient just before applying the effects of Treat Wounds. If you do, you gain a +2 circumstance bonus to your Medicine check to Treat Wounds, and if you roll a success, you get a critical success instead.
We're only 1st level right now, but when I reach 2nd level, I'm considering taking the Assurance feat, which says:
Even in the worst circumstances, you can perform basic tasks. Choose a skill you’re trained in. You can forgo rolling a skill check for that skill to instead receive a result of 10 + your proficiency bonus (do not apply any other bonuses, penalties, or modifiers).
At 2nd level, assuming I improve my Medicine to Expert, my bonus for medicine checks would 4 (for Expert) + 2 (level) + 3 (Wisdom) = +9.
Given that a successful Treat Wounds check only requires me to pass a DC15 check, it seems that by using Assurance I can always guarantee myself a success since my result would default to 19. Could I combine this with Risky Surgery's benefit which stipulates that a regular success becomes a critical success?
Additionally, is it correct to assume that I can't get Risky Surgery's +2 bonus since Assurance bars any other bonuses?
Best Answer
You can Combine Them
Nothing in either ability prevents this combo (though it's worth noting that the damage happens before healing), however you're correct that you wouldn't get the +2 from Risky Surgery with Assurance preventing any modifiers from applying. Further, you also don't add your ability modifier to the skill using Assurance.
So with your example you'd only add your +6 proficiency bonus at level 2 as an expert, still enough to automatically succeed and therefore critically succeed as long as you're using the trained DC of 15 rather than the expert DC of 20, though you wouldn't be able to automatically critically succeed at the expert check until level 6 with a +10 proficiency bonus.
Rolling for the expert DC at level 2 would instead give a +11 modifier, 60% to heal 4d8+10-1d8 (avg. 23.5) with 40% to deal 1d8 damage instead of the guaranteed 4d8-1d8 (avg 13.5), which is fairly fitting for the idea of Assurance allowing you to reliably get something without reaching your maximum.