if I play a poison on one of my unit, did the main action use for play Poison count in it's effect?

If a Bear FrostBack fight something, like a Living Dolls...how resolves the effects? I search but found so many different responses, I would like an official if it's exist.

Same with shadow counter, if we target an unit whose just attack and this unit got an effect like "after attack, etc" but Shadow counter kill it.

When summon Mist Spirit can we summon more than 2 if we use more dices?

Thank you in advance,
sorry for grammar misakes, I am french :/