RulingHall of Heroes (rules 1.0–1.4)

Ultron: Ultron Stage II says “Forced Interrupt: When Ultron attacks you, put the top card of your deck into play…

Question

Ultron Stage II says “Forced Interrupt: When Ultron attacks you, put the top card of your deck into play facedown, engaged with you as a DRONE minion. Until the end of this attack, Ultron gets +1 ATK for each DRONE minion engaged with you.” Is the modification to Ultron’s ATK created by the second sentence of this interrupt “locked in” at the time the interrupt triggers?
Or is it “smart” enough to check throughout the attack and change if the number of DRONES engaged with you changes? Similarly, if the answer to above is the “smart” option, is the player referred to by the “you” at the end of that sentence (“…for each DRONE minion engaged with you”) “locked in” at the time the interrupt triggers? That is, will it remain referring to the player who was the original target of the attack, throughout the attack?
Most specifically: if a player who is not the original target defends one of Ultron’s attacks, will the “you” begin referring to the new target of the attack and recalculate Ultron’s ATK accordingly?

Answer

To answer your question(s):

For Ultron II, your second interpretation seems to line up with the intent of the card. Ultron II would deal you a drone minion when he activates & initiates an attack against you, and until the attack is complete, he would get +1 ATK for each drone attached to you. If you had no drones attached to you and were in hero form when Ultron II activated against you, he would initiate an attack against you, deal you a drone, and have +1 ATK until the attack finished resolving.

If, after Ultron II dealt you a drone, a different hero wanted to defend for you, Ultron II’s attack modifier would depend on the drones that were attached to you, the original player he was activating against. (So if you had one drone attached, and the defender had none, Ultron II would still have +1 ATK when damaging the defending hero.)

— Alex Werner, FFG Game Rules Specialist