I know you can't DIRECTLY poison Steel-type Pokemon, but what about INDIRECTLY?? How about through Trick with Toxic orb or Fling (since Fling is Dark-Type). If these work, please tell me and can anyone tell me any other ways.
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A Pokémon that is currently Poison-type or Steel-type cannot become poisoned, except by Pokémon with the Corrosion Ability; in Generation II only, Twineedle can poison Steel-type Pokémon as well. However, a poisoned Pokémon retains this status condition even if it gains any of these types in battle (or regains the lost type once it is switched out or the battle ends).
source So type changes, twineedle, and corrosion are currently the 3 ways to poison a steel Pokemon in the main series games.
There is only one way to do it with one Pokemon: Kecleon.
An example of doing it is in this scene:
Lucario used Toxic! Kecleon was badly poisoned! Kecleon used Thunderbolt! Kecleon is hurt by poison! Lucario used Iron Tail! Kecleon's Color change made it the steel type!
.....Other than a battle somewhat like this, it's impossible to poison a Steel type.
Don't know what version your on but this should help if it's at least gen 7 :)
A common way to poison steel types, is with the Corrosion ability that the Salandit and Glimmet lines have. I've not yet tested if this extends to a salandit using Toxic Spikes, and then leaving the field. But I know at a bare minimum, Corrosion allows the Pokémon to poison any type with any move that inflicts poison! Hope this helps!
Well there is other ways too. 1. Have a steel type pokemon use toxic on gardevoir. One of its abilties makes it so that if its poisoned then the opponents also poisoned. I know this works cause i once did it on a geodude. 2. Have the opponent hold the ring target. It lets moves that don't effect it hurt the pokemon. 3. have a golduck on your team and read the following:
A wild klink appeared!
golduck used soak! Klink is now a water type!
With this strategy you can change the opponents steel type into a water type, making it able to take poison type moves. Hope this helps!