User blog comment:Aicilespear/Some recommended sets of SP for the Six Heroes (and perhaps more)/@comment-26140304-20160425025121

Fun fact: You can get a minimum of 31 imp runs with Atro.

That being said, if you equip Atro with Phantom Gizmo/Ereborn's Aegis & Sacred Crystal along with Atro's beginning-effects SP skill and an Ophelia/Carrol lead, Atro can get BB on the first turn. As long as Atro has a base Atk of 3300-3400 (with imps, but without any other stat modifications like LS and spheres), his BB can one-shot all of the imps.

If you're worried about Artons showing up, simply take a Mifune (preferably max imped in Atk) and equip him with Sky Harbinger & Shiny Anklet.

Position Atro on the top-left and Mifune in the middle-left. Set Atro on Auto, Mifune on normal attack, and Ophelia/Carrol and friend lead to Guard. Note that guarding doesn't affect the performance of units.