If I roll a successful attack roll, then a damage roll that is greater than the remaining HP of a monster, do I have to apply all of it or can I leave him at 1 or even 0 HP? It doesn't Instant Kill him.
Basically, I want to interrogate the goblin at the beginning of the starter set for 5e and he only has 1 HP left before I roll this hypothetical roll.
Do I have any other options? (such as a capture or something like that)
Best Answer
Yes, you must apply all the damage--but you can still leave your target alive. Except in the case of instant death: "when damage reduces [one] to 0 hit points and there is damage remaining, [one dies] if the remaining damage equals or exceeds [one's] hit point maximum." (PHB p.197)
Clearly any melee attack1 can be optionally declared incapacitating rather than lethal. However, the conclusion to draw from the earlier section is that even ranged attacks don't immediately kill a monster: you've got time to stabilize the goblin just as you would an ally. It's just that rarely anyone ever tracks it, and for ease of play we just leave a wide swath of assumed-dead opponents in our wake. (But you may not want to leave that wake: I suggest this as a way to keep your PCs from becoming a bunch of murderous cretins.)
1 - note that this includes melee spell attacks; clarification in November 2015 Sage Advice