If a unit with 4 Might and a buff (making it 5 Might) is moved to a battlefield, the opponent reacts with Smokescreen (giving -4 Might), and then Sett's champion ability is used to spend the buff and recall the unit, will the unit survive as a 0 Might unit?

Ruling: Yes, the unit will survive. A unit only dies when it has damage marked on it equal to or greater than its Might. Having 0 Might does not cause death if there is no damage marked on it.

Sequence:

• Unit with 4 Might and a buff (5 Might total) moves to battlefield
• Opponent uses Smokescreen, giving -4 Might (unit becomes 1 Might)
• Sett's ability spends the buff and recalls the unit to base, healing it
• Unit is now 0 Might (4 base Might - 4 from Smokescreen) with no damage marked
• Unit survives because it has no damage marked on it

Nuances:

• Smokescreen's -Might effect lasts until end of turn and is not removed by healing
• Healing only removes damage, not -Might effects
• Lethal damage requires a non-zero amount of damage marked on a unit
• Future sets will have -Might cards without the minimum 1 Might limit, making this interaction more common
• If a unit has damage marked equal to its Might, spending a buff that was increasing its Might would cause it to die