Giga Drain got a buff, but I still don't think it's worth using not boosted anyways. Evil Eye and Venom Shock are quite powerful with toxic spikes. Brelooms aren't much of a problem anymore since many have Technician and get shocked with venom. Since it was noted before how Disable forces switches, this could get more Pokemon poisoned, and each time they come back in they immediately take 1/16 or 1/8 of their health while Gengar was using Slack Off with a relaxed nature. Maybe they take more if more hazards are up.