The Lordvessel

Whenever a legendary creature dies, put X soul
counter on The Lordvessel, where X is half its mana
value (rounded down).

{t}: Add one mana of any color. Activate only
if The Lordvessel has at least a soul counter.

{t}, Remove X soul counter from The Lordvessel:
search your library for a legendary creature with
mana value X and put it into your hand.