Krosh, the Half Purified

+1: Each player loses 1 life. Draw a card for each 1 life lost this way.
-3: Destroy target creature. Create an X/X black sliver creature token, where X was the destroyed creature's converted mana cost.
-7: Destroy all cretures. Then create an X/X black sliver giant creature token, where X is the total converted mana cost of the destryoed creatures.