You're correct that poison will do nothing if you don't let FK get a turn, unless you happen to run someone with a poison explode move. I used to do that with a similar team, with Alure keeping him from getting a turn, and Karam for poison explode.

As for heal - if you have effects like continuous heal, I am fairly certain they will activate only after the poison damage. So, if they die to poison, they won't get the heal. Is that what you're asking?

Thanks, yes, I was using Zavia for poison explode, but mine is a bit squishy for 20+ levels of FK.

As for healing, I was asking for the exact moment when healing happens. Is it at the start of (any) champins turn? 

But the thing you wrote is important, too, if you have poison and healing on the same champion. Will have to see in what order these two things activate. Or is it simply the order they were placed?

Honestly - it could be either. It's rare to be in a situation where it would matter, so I can't really confirm one way or another.

But as for healing - continuous heal buffs specifically, will heal at the start of the champ's turn. Also, effects like the Immortal or Regen sets will also activate at the start of their turn.

However, there are some healing effects which will activate at other times. The best example of this is the Shadow Heal mastery, which activates whenever an enemy gets healed. That heal activates at the moment the enemy is healed. However, do note that if they are healed by Lifesteal/Leech, the heal only happens after the damage is dealt, so it won't save you if the damage would have otherwise killed you.