So this is a list of pokemon I have tested out and can say they are good for great league, so lezgo!
Grumpig: Very well rounded, and it has shadow ball, so thats a plus.
Toxicroak: You probably expected this.
Medicham: You must’ve expected this.
Castform: Normal: Tackle Energy Ball.
Fire: Ember Solar Beam.
Water: Water Gun, Hydro Pump, along with Thunder.
Snow: Powder Snow, Blizzard.
Suicune: If you have some fron your Weekly box, power it up to great league standards.
Bellossom: Acid, Leaf Blade, Dazzling Gleam, it works.
Mawile: Bite, Play Rough, lron Head, decent attack stat for that low of cp.
Clefable: Charge Beam, Dazzling Gleam, Psychic, it’s decent.
Raichu: Alola or Kanto form works, just make sure it has Wild Charge.
Tauros: Zen Headbutt, Earthquake, Iron Head.
Eevee: Quick Attack, Dig, Last Resort (Swift if not available)
Azumarill: Very Tanky, Rock Smash, Hydro Pump, Ice Beam.
Gen 1 bug types: any moveset.
Kingler: People have been wanting a better move on this for two years now.
Ivysaur: Solar Beam? Razor Leaf? Perfection has ensued.
Sunflora: Razor Leaf, Solar Beam, Sludge Bomb.
I hope that helps, and keep stacking up on those SS’s!