Cnidali doesn't seem that amazing. It's reasonably bulky, but Psychic, Ground and Flying attacks murder it so that's dangerous in a Gardevoir/Braviary/Musharna/Golurk metagame. It's got an excellent support movepool and the bulk to use it, but at the same time there are a lot of things that easily shut it down. In fact, Golurk stomps it six ways to Sunday unless it's running Ice Punch or Crunch. It'd likely replace Garbodor and reduce usage of Butterfree, and will be a nice pivot... but I don't see it as gamebreaking so far, especially since it can't really scratch Ghosts without several BU boosts or Crunch, and if it runs Crunch it means it's not running Toxic Spikes or Rapid Spin.
Also, why does a Poison type even have Poison Heal?