Debt of Loyalty

Regeneration as a theft mechanic: the design conceit is that a creature about to die owes its survival to you, and the debt is paid in control. The trick depends entirely on the regeneration shield actually firing. Cast it on its own and nothing happens; the targeted creature has to take lethal damage or hit a destroy effect while the shield is up, at which point it taps, removes all damage, and switches sides. That conditional is the concession that lets white have a permanent steal at all: you only profit when the regeneration matters, so the effect never resolves into free value. To take an opposing attacker, you point it at that attacker and wait for combat damage or removal to trigger the shield; the more reliable line is floating it in response to a destroy effect aimed at a creature an opponent values, turning their own removal into your acquisition. Instant speed is what makes this work as a theft spell rather than a defensive regeneration trick: the window is narrow, tied to a death event you do not fully control, and that timing requirement is what prices the effect. White rarely gets to keep a creature it did not cast, and the whole spell is built around the one moment where saving a creature and stealing it become the same action.