How do you get the TM mean look in Pokemon Platinum?
Where do you get the psychic TM in platinum?
What does a mean look do on a Pokemon?
Mean Look prevents the target from switching out or fleeing (including via Teleport). It bypasses accuracy checks to always hit, unless the target is in the semi-invulnerable turn of a move such as Dig or Fly. The effect only applies as long as the Pokémon that used it remains in battle.
A Pokémon with the Ability Shadow Tag prevents opposing Pokémon from attempting to flee. (From Generation IV onward, Pokémon with Shadow Tag are unaffected by Shadow Tag.) A Pokémon with the Ability Arena Trap prevents opposing grounded Pokémon from attempting to flee.
Gengar’s moveset has been shifted around dramatically over the decades, but currently, Mean Look can be learned by Gastly at level 8 and carried over to Gengar when it evolves.
Golbat is your best bet. You can catch high level ones – often ones that already have Mean Look – in Victory Road.