Clavilenio last of the blessed

When this creature enters, you may gain any amount of life. If you do, lose life until you have 20. You cannot play cards with lower mana value than the amount of life you gained.

If you gain exactly x life, choose one and sacrifice this creature.
Gain 1 life for each permanent in play, then sacrifice all creatures you control

Each opponent loses half their life, rounded of then gains x life.