Stifle

Counter target activated or triggered ability. (Mana abilities can't be targeted.)

Mox Opal

Metalcraft — {T}: Add one mana of any color. Activate only if you control three or more artifacts.

Phyrexian Dreadnought

Trample
When Phyrexian Dreadnought enters, sacrifice it unless you sacrifice any number of creatures with total power 12 or greater.

Illusionary Mask

{X}: You may choose a creature card in your hand whose mana cost could be paid by some amount of, or all of, the mana you spent on {X}. If you do, you may cast that card face down as a 2/2 creature spell without paying its mana cost. If the creature that spell becomes as it resolves has not been turned face up and would assign or deal damage, be dealt damage, or become tapped, instead it's turned face up and assigns or deals damage, is dealt damage, or becomes tapped. Activate only as a sorcery.

Underground Sea

Polluted Delta

{T}, Pay 1 life, Sacrifice Polluted Delta: Search your library for an Island or Swamp card, put it onto the battlefield, then shuffle.

Vault of Whispers

Hunted Horror

Trample
When Hunted Horror enters, target opponent creates two 3/3 green Centaur creature tokens with protection from black.

Torpor Orb

Creatures entering don't cause abilities to trigger.

Lotus Petal

{T}, Sacrifice Lotus Petal: Add one mana of any color.

Dark Ritual

Dress Down

Flash
When Dress Down enters, draw a card.
Creatures lose all abilities.
At the beginning of the end step, sacrifice Dress Down.

Death's Shadow

Death's Shadow gets -X/-X, where X is your life total.

Sundial of the Infinite

{1}, {T}: End the turn. Activate only during your turn. (Exile all spells and abilities from the stack. Discard down to your maximum hand size. Damage wears off, and "this turn" and "until end of turn" effects end.)

Seat of the Synod

Darkslick Shores

Darkslick Shores enters tapped unless you control two or fewer other lands.
{T}: Add {U} or {B}.

Scroll of Fate

{T}: Manifest a card from your hand. (Put that card onto the battlefield face down as a 2/2 creature. Turn it face up any time for its mana cost if it's a creature card.)