4 or 8, depending on which opponent your partner chooses to assign the damage to. If he assigns it to the cursed player, it will be doubled. If not, then it won't.
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Bio-units terminate noise exchange. It is time for you to ingest sandwiches from my compartment.
To expand a bit on why it works this way: in 2HG, you attack the opposing team, as a team. But when it comes time for the combat damage, you assign each creature's damage to one of the players on that team. The damage ends up affecting the team's shared life total, but since there are effects in Magic which care specifically about which player was dealt damage, you choose one of the players to actually assign the damage to.
So in your case, you probably want to be assigning the combat damage to the player enchanted by the Curse, since that'll cause the Curse's effect to apply to that damage.
EDH - Ghave, Guru of Spores
EDH - Rafiq of the Many
EDH - Roon of the Hidden Realm
-Griff
So in your case, you probably want to be assigning the combat damage to the player enchanted by the Curse, since that'll cause the Curse's effect to apply to that damage.
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Lightning Bolts don't kill creatures. State-based actions kill creatures.