Pokémon Power: Transparency
Whenever an attack does anything to Haunter, flip a coin. If heads, prevent all effects of that attack, including damage, done to Haunter. This power stops working while Haunter is affected by a Special Condition.
[P][C] Nightmare: 10
The Defending Pokémon is now Asleep.
Because of its ability to slip through block walls, it is said to be from another dimension.