Ability · Gen 4 · 6 Pokémon
Forewarn
On switch-in, this Pokemon is alerted to the foes' move with the highest power.
On switch-in, this Pokemon is alerted to the move with the highest power, at random, known by an opposing Pokemon. This effect considers OHKO moves to have 150 power, Counter, Mirror Coat, and Metal Burst to have 120 power, every other attacking move with an unspecified power to have 80 power, and non-damaging moves to have 1 power.
Forewarn was introduced in Generation 4. 6 Pokémon and forms can have it.
Best Pokémon with Forewarn
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 Forewarn.
Pokémon with Forewarn
As a regular ability (6)
Drowzee
Hypno
Jynx
Smoochum
MunnaForewarn FAQ
What does Forewarn do?
On switch-in, this Pokemon is alerted to the move with the highest power, at random, known by an opposing Pokemon. This effect considers OHKO moves to have 150 power, Counter, Mirror Coat, and Metal Burst to have 120 power, every other attacking move with an unspecified power to have 80 power, and non-damaging moves to have 1 power.
Which Pokémon have Forewarn?
6 Pokémon and forms can have Forewarn: Drowzee, Hypno, Jynx, Smoochum, Munna and Musharna.
What are the best Pokémon with Forewarn?
By competitive usage, the most used Pokémon that can have Forewarn are Musharna (#271 in Champions VGC, 8.7% run Forewarn).
Effect text from Pokémon Showdown (MIT); which Pokémon have it from Showdown's Pokédex, cross-checked against PokéAPI. Unofficial fan site.