Havi, the All-Father

Sage Project is the whole engine, and it climbs downward. The trigger fires whenever this or another of your legendary creatures dies, and it only reaches back for a legendary creature of lesser mana value: never sideways, never up. That descending constraint is what pays for a repeatable reanimation trigger sitting on a self-protecting body. You cannot chain-return the same big threat forever; each death buys back something cheaper, so value flows in one direction until the pile is picked clean. The indestructibility rider works as a threshold rather than a static keyword: it wants four or more historic cards in the yard (artifacts, legendaries, and Sagas all qualify), exactly the fuel a legendary-heavy shell is already generating on its way to feeding the recursion. The two abilities describe the same deck from opposite ends. One asks you to sacrifice, self-mill, and grind through your own legends; the other rewards you for having done so with a 6/6 that stops dying. What makes it worth building around is the timing: the trigger keys on death, not on cast or attack, so removal pointed at your legends stops being a clean answer. Kill one, and the corpse pulls another off the pile, tapped but alive; the opponent has now traded their removal to shrink your graveyard while advancing your board. It turns attrition into an accounting problem they have to solve twice.