Helm of Possession

Control magic structured as an engine rather than a single permanent steal, and the design discipline is entirely in the keep-tapped clause. Holding a creature means the Helm stays tapped and locked out of its untap step, so seizing a fresh target requires first deciding to untap, which immediately ends the current control effect and returns the held creature before the new activation can even begin. That ordering turns the artifact into a sequence of trades rather than a stockpile: you can never bank two creatures, only swap which one you point at, and each swap costs you a body to sacrifice plus the and the tap. The natural play pattern writes itself: feed it an expendable creature to grab the biggest threat across the table, then sacrifice the next bit of fodder to re-aim when something better appears. Unlike enchantment-based theft such as Control Magic, which dies to enchantment removal and frees the creature, this is an artifact that can choose to keep its grip indefinitely or release and re-aim on its own terms. Destroying the Helm is the built-in pressure valve: blow it up and the held creature comes home at once. It rewards a board with cheap bodies to spend and punishes opponents whose best creature is also their only creature, since the Helm will keep pointing at it.