The Strongest Pokemon That's Not Legendary Is Slaking
Because Once I Put Him On Level Lv100 And Used Protien
On Him And His Attack Was 418(Lonely Nature)So Try And Evolve Him From Vigoroth Also If You Wanna Catch Wild Pokemon That You Can't Find Have A Pokemon That Has A Truant Effect Like Slakoth or Slaking Go Near The Wild Pokemon's Location And If You Hear A Pokemon Make A Noise Search In The Grass In That Location Or Cave
And It Will Be The Wild Pokemon You Wanna Catch!

This Hint Really Works!