Immortal Coil

The third ability checks whether your graveyard is empty only at the time it triggers. Putting a card into your graveyard after that doesn’t help. You’ll lose the game when the ability resolves.

The second ability prevents all damage that would be dealt to you, regardless of how many cards are in your graveyard. For example, if you have three cards in your graveyard and would be dealt 5 damage, Immortal Coil prevents all 5 damage and exiles all the cards in your graveyard.

Similarly, if the third ability resolves but you don’t lose the game for some reason (because you control Platinum Angel, perhaps), it will immediately trigger again if your graveyard is still empty. Immortal Coil + Platinum Angel + an empty graveyard is an involuntary infinite loop. Unless a player disrupts it, the game will end in a draw.