Fanatical Devotion

The trade is brutal and unconditional: feed it a creature, save a creature, and pay nothing in mana to do it. That last part is the whole point. A regeneration shield that costs no mana to fire is one you can raise on the turn you tapped out, again and again, until your board runs dry. That makes it less a single safety net than a conversion engine: every creature you control becomes potential protection for the one that matters, whether that is a token-spewing threat, a fragile combo piece, or the lone blocker holding the line. What it cannot do is a property of regeneration itself, not of the cost. Regeneration only intercepts destruction and lethal damage; it does nothing against exile, nothing against bounce, nothing against a -X/-X that drops toughness to zero. So the outlet's value splits cleanly between two jobs that rarely overlap on the same turn: leaving one creature standing through a board wipe that destroys, and serving as a free, repeatable sacrifice trigger for whatever death-matters payoff sits beside it. The regeneration is almost incidental to that second role; the sacrifice is the resource. White rarely gets an unconditional, mana-free sacrifice outlet at all, and that scarcity is what keeps the card in conversation well past the regeneration text it advertises.