The planner seems to be indicating that Nightfall in the Scrapper Ancillary Darkness Mastery accepts the following IO sets:
* Ranged (AoE)
* ToHit Buff
Not sure if that's a goof that was also made in game since I don't have any scrappers with that set, but it should be showing:
* Ranged (AoE)
* ToHit Debuff
* Accurate ToHit Debuff