On the third attempt, I decided to lead with Gastly and immediately used Curse on Lurantis. This time, the Lurantis SOS-called Kecleon first instead of Comfey. I had Gastly use Hypnosis on Kecleon to prevent it from setting up Sunny Day, then Lurantis KO'd Gastly. I sent out Cutiefly, and without the Sun up and with Curse damage adding up, this time Lurantis couldn't out-heal Cutiefly's Bug Buzz damage. Cutiefly KO'd Lurantis while Kecleon stayed asleep, then I brought in Crabrawler to KO Kecleon and finish the battle without the Comfey ever being called in.