Herbal Poultice

Free to play, but never free to use: the zero-cost casting is a bookkeeping convenience for an artifact whose real price lands on the activation, where plus the sacrifice buys a single regeneration shield. The cost has simply migrated from the table to the ability, and it is an expensive rate for the effect even in an era when regeneration was the dominant way to keep a creature alive in combat. The one-shot nature seals the bargain: it answers exactly one removal spell or one bad block before it is gone. What the zero mana value does buy is presence. The artifact can sit on the board through a turn it costs nothing to deploy, so the regeneration waits as a held option without tapping you out, which matters when that activation is the only line item your opponent has to play around. Utility filler built to round out an artifact subtheme and hand a fragile creature deck a cheap-to-include insurance policy, with the protection priced deliberately high so it never warps a board the way free or repeatable regeneration would. The activated cost is doing the balancing work the casting cost refuses to: a regeneration effect you can drop for nothing has to be slow and disposable to use, and this one is both.