Newbie question for below 2 cards:

Thief of essence

Action: When one or more units leaves play, draw a card.

Q1 Even when opponent's units leaves play, I could draw a card? (I assume yes)

Take captive

Action: Take control of target attacking unit until the end of the turn. Move it to the attacked zone, declared as a defender.

Q1. If I take control of Swarm of bats as defender, after battle, will it go to my discard pile?

Q2. If I take control of Doombull as defender

(Action: When this unit leaves play, deal 4 damage to target unit in any corresponding zone.)

After battle, it dies.

Could I activate its ability to deal 4 damages? Or my opponent will activate this?

Declar as attacker

Q1. Could I declare a unit as attacker if it did not contain hammer icon, or due to some reasons, it's hammer icons were eliminated

Thank you so much.

Q1. Yes. (Imagine how strong this unit is in multiplayer...)

Take Captive

Q1. No.

Q2. Not really sure about this one.

Declare as Attacker

You may declare a unit as an attacker even if it has not power, whether it's printed with no power or has lost its power due to some card effect. Oh yeah, those hammers are power.

Thank you:)

1) Cards always go to their owner's out of play zones (hand, discard pile, deck).

2) The player who last controlled a card while it was in play gets to trigger "leaves play" effects.