Template:UpgradeControl
From Archon Arcana - The KeyForge Wiki
Upgrades enter play under the control of the player who played the upgrade. For THISPAGE, this means that it doesn't matter if it is attached to a Friendly or Enemy creature, the "You/Your" in the constant ability text refers to the person who played the card, regardless of which player controls the creature to which the upgrade is attached. [1].