>>56003419>Lvl 13 0 SpA 0 IVs Oshawott Water Gun vs. Lvl 13 0 HP 0 IVs / 0 SpD 0 IVs Lillipup: 10-13 (29.4 - 38.2%) -- 84.4% chance to 3HKO> +3 Lvl 13 0 Atk 0 IVs Lillipup Tackle vs. Lvl 13 0 HP 0 IVs / 0 Def 0 IVs Oshawott: 28-34 (75.6 - 91.8%) -- guaranteed 2HKOThat Lillipup needs at least 4 Work Ups to start one-shotting your starter, or needs to rely on bite flinches otherwise. Your starter meanwhile can three shot it back, assuming the worst possible luck, which is more than enough to beat Cheren, especially with the rest of your Pokémon in the back.
This thing comes with Helping Hand. Stop trying to gas Gen 5.