You get it once you find the girl and play hide and seek with her on the S.S. Anne
You must Trade Onix while it is holding a Metal Coat in order to Evolve into a Steelix.
Trade it whilst it is holding a Metal Coat.
To get a Steelix, making it hold a Metal Coat
you have to make an onyx hold a metal coat and then trade it.
if the user uses a special based attack on the same round the foe did mirror coat it the user or the get twice the damage
Onix > trade w/ Metal Coat > Steelix
You have to trade your Syther with a Metal Coat to get it to evolve into Scizor.
You need to give it metal coat and trade to evolve it to Steelix.
Make it hold a Metal Coat and trade it. I recommend you to ask someone to trade Scyther with a Metal Coat to you.
The Pokémon that can learn both Counter and Mirror Coat in Pokémon Black would be Wynaut, Wobbuffet and Deoxys however Mudkip is capable of being born with both since both Counter and Mirror Coat are Egg Moves for it which means both of Mudkip's evolutions of Marshtomp and Swampert would be able to both know Counter and Mirror Coat.
Scyther evolves when traded while holding a metal coat.
You will need to use males of either of the following Pokemon which are Squirtle, Blastoise, Wartortle, Marshtomp, Mudkip, Swampert, Feebas, Milotic, Corsola, Gastrodon, Shellos and Alomomola so that you can breed with Milotic so that a Pokemon Egg will hatch into a Pokemon called Feebas that knows the Mirror Coat move.