If I Moonlight Affliction my opponent's Voracious Gromp, does it die?

Whether a Voracious Gromp dies when targeted by Moonlight Affliction depends on whether the unit has any existing damage marked on it at the time the spell resolves.

The Ruling

A unit only dies if the damage marked on it is equal to or greater than its current Might (Rule 142.3, FAQ #2141). Simply reducing a unit's Might—even to 0 or less—does not cause it to die instantly (FAQ #5831).

• Voracious Gromp has a base Might of 5.
• Moonlight Affliction grants a unit -10 Might.

If you cast Moonlight Affliction on an undamaged Voracious Gromp:

1. The Gromp's Might is reduced by 10. Since its base is 5, its Might effectively becomes 0 for the duration of the turn.
2. Because it has no damage marked on it, it remains on the board with 0 Might (FAQ #5831).

However, if the Voracious Gromp already has 1 or more damage marked on it, it will die as soon as its Might is reduced to a value equal to or less than the marked damage (FAQ #2662, FAQ #3880).

Note: I could not fully verify this ruling against the retrieved rules.