Call the Bloodline

The trick to this engine is that it turns excess into board presence at a fixed exchange rate: one card from hand, one mana, one lifelink body, once per turn. That last clause is the real governor. Without the once-per-turn lock, a two-mana enchantment that converts cards into creatures would be a combo piece; the rate-limiter forces it to grind rather than explode, which is precisely the speed at which a slow, attrition-minded black deck wants to operate. What makes the conversion worth paying for is the destination of the discarded cards. Lands you've flooded into, spells dead against the matchup, and especially creatures with graveyard-relevant text all become a 1/1 with lifelink instead of rotting in hand, and the discard is a cost you're paying anyway when you'd rather have the card in the yard than in your grip. The lifelink keyword does quiet work too, padding a life total against the same aggressive decks that punish you for spending a card and a turn on a single small token. It is an enchantment built for the long game: a persistent outlet that asks nothing flashy of you, just a steady willingness to trade the cards you no longer need for chump blockers, sacrifice fodder, and a slow drip of life.