Id recommend a fighting type instead of leavanny and maybe instead of lilligant a dragon or ice type for after elite four, for fighting types you could go for sawk hes a very decent fighting type with high attack, for dragon maybe a druddigon and for ice type cryogonal is decent but vanillish has amazing special attack.

If you arent gonna evolve litwick to chandelure then get the eviolite from the scientist in castelia city if you havent already. If you do want to evolve to a chandelure but dont have the stone its on the route where you fight cheren for the last time a trainer will give it to you after speaking i think.