T.O.W.A.N.

Try using sheer force Nidoking with earth power and flamehthrower and equip it with the life orb. Or you could try changing the terrain. Roserade and gloom learn grassy terrain via level up, while the venusaur line learns it from breeding. Lead off with either roserade, gloom/vileplume, or venusaur, equip it with a magical seed so that the alolan sandslash won't destroy it on turn one, then use grassy terrain. Then, switch out to sheer force Nidoking, a dragalge that knows flamethrower, or a salazze, and spam field boosted fire attacks. 

This game does have scripting issues. I've lost my first save file because I saved during the cutscene where  Reukra retires from from being heckled by protesters. Since he freezes at the staircase, I can't continue the game.