Ability · Gen 4 · 2 Pokémon
Bad Dreams
Causes sleeping foes to lose 1/8 of their max HP at the end of each turn.
Causes opposing Pokemon to lose 1/8 of their maximum HP, rounded down, at the end of each turn if they are asleep.
Bad Dreams was introduced in Generation 4. 2 Pokémon and forms can have it.
Best Pokémon with Bad Dreams
Ranked by usage in public Pokémon Showdown battles (Champions VGC first, then National Dex OU, SV OU and Champions Singles), with how many of each Pokémon's sets actually run Bad Dreams.
Pokémon with Bad Dreams
As a regular ability (2)
Bad Dreams FAQ
What does Bad Dreams do?
Causes opposing Pokemon to lose 1/8 of their maximum HP, rounded down, at the end of each turn if they are asleep.
Which Pokémon have Bad Dreams?
2 Pokémon and forms can have Bad Dreams: Darkrai and Mega Darkrai.
What are the best Pokémon with Bad Dreams?
By competitive usage, the most used Pokémon that can have Bad Dreams are Darkrai (#21 in SV OU, 100% run Bad Dreams).
Effect text from Pokémon Showdown (MIT); which Pokémon have it from Showdown's Pokédex, cross-checked against PokéAPI. Unofficial fan site.