Zeromiz

This is the strategy I used to beat Morty's Haunter: Use Stantler's hypnosis on Haunter, since it will want to use sucker punch on Stantler, which is the only move Haunter can use to damage Stantler. Once it falls asleep, you can switch to your other pkmn to take it out. Switch back to Stantler after 2-3 turns if you think Haunter will wake up. Repeat until Haunter faints.