Creeping Tar Pit

Creeping Tar Pit enters the battlefield tapped.
{T}: Add {U} or {B}.
{1}{U}{B}: Creeping Tar Pit becomes a 3/2 blue and black Elemental creature until end of turn and can't be blocked this turn. It's still a land.

Spire Mangler

Flash
Flying
When Spire Mangler enters the battlefield, target creature with flying you control gets +2/+0 until end of turn.

Nimble Obstructionist

Flash
Flying
Cycling {2}{U} ({2}{U}, Discard this card: Draw a card.)
When you cycle Nimble Obstructionist, counter target activated or triggered ability you don't control.

Island

Omen of the Sea

Flash
When Omen of the Sea enters the battlefield, scry 2, then draw a card.
{2}{U}, Sacrifice Omen of the Sea: Scry 2.

Slitherwisp

Flash
Whenever you cast another spell that has flash, you draw a card and each opponent loses 1 life.

Serum Visions

Duress

Target opponent reveals their hand. You choose a noncreature, nonland card from it. That player discards that card.

Capture Sphere

Flash (You may cast this spell any time you could cast an instant.)
Enchant creature
When Capture Sphere enters the battlefield, tap enchanted creature.
Enchanted creature doesn't untap during its controller's untap step.

Swamp

Cunning Nightbonder

Flash
Spells with flash you cast cost {1} less to cast and can't be countered.

Jwar Isle Refuge

Jwar Isle Refuge enters the battlefield tapped.
When Jwar Isle Refuge enters the battlefield, you gain 1 life.
{T}: Add {U} or {B}.

Brineborn Cutthroat

Flash (You may cast this spell any time you could cast an instant.)
Whenever you cast a spell during an opponent's turn, put a +1/+1 counter on Brineborn Cutthroat.