Sunken Depths

Sunken Depths comes into play tapped.
{t}: Add {u} to {b} your mana pool.
{2}{u}{b}: Sunken Depths becomes a 1/1 elemental
creature with flying and "When this creature
deals damage to a opponent, that opponent must
reveal their hand."
Many secrets lie in wait here, and only the bravest
dare to tread its dangerous landscape.