Let's say I have ten developments in my battlefield and my opponent has none. I play Veteran Sellswords, then equip them with a Hellblaster Volley Gun. At the end of my turn, my opponent gains control of the Sellswords. Now, do the Sellswords do +10 damage in combat, or +0? In other words, does Hellblaster Volley Gun count the developments of the owner or the controller?

RM

Attach to a Target Unit in your Battlefield. Attached Unit deals +X damage in combat, where X is the number of developments in your Battlefield.

To me I'd say since it says "Your Battlefield" that would refer to the controler of 'Hellblaster Volley Gun'. (so in this case the Sellsword would do +10 for both you and your opponent)

Vitamin T said:

I was with you until the parenthetical at the end. Once the Sellswords swings to the other side it and the Hellblaster are controlled by them. When they attack they check "their battlefield" which has no developments and as a result no extra damage is inflicted.

Why would control of the Hellblaster change? You are allowed to play attachments on an opposing unit, so if the sellswords change control the person who played the hellblaster should still control it. (as far as I can tell)

You've played the attachment, you keep control of the attachment even if the control of the unit changes.

There is nothing in the rulebook stating that control of attachment changes with the control of an unit.