Mana Short

Tap all lands target player controls and that player loses all unspent mana.

Island

Mishra's Helix

Dimir Infiltrator

Dimir Infiltrator can't be blocked.
Transmute {1}{U}{B} ({1}{U}{B}, Discard this card: Search your library for a card with the same mana value as this card, reveal it, put it into your hand, then shuffle. Transmute only as a sorcery.)

Swamp

Minister of Impediments

({W/U} can be paid with either {W} or {U}.)
{T}: Tap target creature.

Pooling Venom

Enchant land
Whenever enchanted land becomes tapped, its controller loses 2 life.
{3}{B}: Destroy enchanted land.

Psychic Venom

Enchant land
Whenever enchanted land becomes tapped, Psychic Venom deals 2 damage to that land's controller.

Benthic Explorers

{T}, Untap a tapped land an opponent controls: Add one mana of any type that land could produce.

Seizures

Enchant creature
Whenever enchanted creature becomes tapped, Seizures deals 3 damage to that creature's controller unless that player pays {3}.

Deceiver Exarch

Flash (You may cast this spell any time you could cast an instant.)
When Deceiver Exarch enters, choose one —
• Untap target permanent you control.
• Tap target permanent an opponent controls.

Reality Spasm

Choose one —
• Tap X target permanents.
• Untap X target permanents.

Sunken Hollow

({T}: Add {U} or {B}.)
Sunken Hollow enters tapped unless you control two or more basic lands.