The cards required:
Card Title: Notorious Assassin
Casting Cost: 3B
Pow/Tgh:
2/2
Card Text: 2B, Tap, Discard a card from your hand: Destroy target
nonblack
creature. It can't be regenerated.
Rarity: R
Expansion: Mercadian Masques
Card Title: Bog Witch
Casting Cost: 2B
Pow/Tgh:
1/1
Card Text: B, Tap, Discard a card from your hand: Add BBB to your
mana pool.
Rarity: C
Expansion: Mercadian Masques
The strategy:
If you use a graveyard-play deck, this strategy should help you.
First, tap a swamp and discard a card, use Bog Witch's ability to get the 3
black mana, then use the 3 mana for Notorious Assasssin's ability to destroy an
opponent's creature. So then, you add two cards into your graveyard for
threshold or whatever you would do to them in the graveyard, and also get to
destroy a nonblack creature, for 1 mana!