Knight of Death and Despair

Shroud
As long as this card isnt a creature, it cant
attack or block.
Whenever a spell you cast makes you lose life,
this card becomes a creature and gains indestructible.
Whenever this creature attacks or blocks, target
player may pay X life,
where X is twice the life you lost this turn.
If they dont, destroy up to X target creatures
with total mana value X or less