Caustic Mist reads: "Place a 3" AOE cloud effect completely in this model's ctrl area. A model entering or ending its activation in the AOE suffers 1 point of corrosion damage. Lasts for 1 round."
1) Bane Knights charge Temple Flame Guard
2) Combat is resolved
3) Bane Knight activation ends
4) eGaspy activates and casts Caustic Mist, placing the 3" AOE so that some BK and some TFG are covered with it
Since the spell says models entering or ending its activation take damage, would the BK take damage since their activation already ended? I'd like to use this tactic in games so that if the enemy moves they take a free strike, and if they stay they die.