Sickening Shoal

You may exile a black card with mana value X from your hand rather than pay this spell's mana cost.
Target creature gets -X/-X until end of turn.

The Ur-Dragon

Eminence — As long as The Ur-Dragon is in the command zone or on the battlefield, other Dragon spells you cast cost {1} less to cast.
Flying
Whenever one or more Dragons you control attack, draw that many cards, then you may put a permanent card from your hand onto the battlefield.

Nourishing Shoal

You may exile a green card with mana value X from your hand rather than pay this spell's mana cost.
You gain X life.

Blazing Shoal

You may exile a red card with mana value X from your hand rather than pay this spell's mana cost.
Target creature gets +X/+0 until end of turn.