Elusive and advantage canceling?

[Sindeloke]

So say we have a level 20 rogue, in melee combat with, idk, a giant snake, in the middle of a pitch black room. The snake makes some kind of trip attack and manages to knock the rogue on her butt. This entitles it to a bonus attack.

How many dice does the snake roll for this attack? Or, more on point, when does Elusive kick in?

If it applies after all other calculations, the snake has advantage (against a prone foe) and disadvantage (because it can't see), which cancel out. Elusive doesn't apply and is irrelevant to the scenario. It rolls one die.

But if it applies individually to any instance of advantage, the snake has advantage (against a prone foe) and then loses that advantage (because you can't have advantage on the rogue). We then apply the disadvantage from blindness and the snake is rolling two dice and taking the lowest.

My inclination as a DM is to apply Elusive first, otherwise you basically end up denying the rogue a class feature half the time, but that's just an off-the-cuff instinct.

[Chen]

From the Advantage/Disadvantage section we have:

"If circumstances cause a roll to have both advantage and disadvantage, you are considered to have neither of them..."

From Elusive:

"No attack roll has advantage against you while you aren't incapacitated"

If you have Elusive (and are not incapacitated) an attack roll can never have advantage against you. As such the circumstances quoted above in the Advantage/Disadvantage section cannot occur. There is no way for a roll to have both advantage and disadvantage because it can never have advantage. As such, I'd say the snake would just have the disadvantage.

Note this does imply that there is no way to mitigate attack roll disadvantage against an elusive rogue (barring incapacitation). I don't think that's unreasonable, or unbalanced for an 18th level ability though.

[Easy_Lee]

From Elusive:

"No attack roll has advantage against you while you aren't incapacitated"

If you have Elusive (and are not incapacitated) an attack roll can never have advantage against you. As such the circumstances quoted above in the Advantage/Disadvantage section cannot occur. There is no way for a roll to have both advantage and disadvantage because it can never have advantage. As such, I'd say the snake would just have the disadvantage.

I believe this is the correct ruling. Elusive prevents advantage from being possible at all, meaning it is removed from the equation. So having both advantage and disadvantage against an elusive target results in disadvantage, not neutral, because the attacker doesn't actually have advantage.

[pwykersotz]

I side with the interpretation that gaining advantage and having advantage are two different things. I think Elusive only prevents the actual rolling of 2d20 and taking the highest, not offsetting disadvantage. I'm open to thoughts on it though, that's just how I read it initially.