Arctic Flats

Arctic Flats enters tapped.
{T}: Add {G} or {W}.

Brood Sliver

Whenever a Sliver deals combat damage to a player, its controller may create a 1/1 colorless Sliver creature token.

All Slivers have "{T}: Target Sliver creature gets +X/+0 until end of turn, where X is the number of Slivers on the battlefield."

Abraded Bluffs enters tapped.
When Abraded Bluffs enters, it deals 1 damage to target opponent.
{T}: Add {R} or {W}.

Whenever a Sliver deals damage, its controller gains that much life.

Sliver creatures you control have flying and haste.

This land enters tapped.
When this land enters, you gain 1 life.
{T}: Add {G} or {W}.

Sliver creatures you control have "When this creature enters, it deals 1 damage to target player or planeswalker and you gain 1 life."

{T}: Add one mana of any color. Spend this mana only to cast a creature spell.

All Sliver creatures have "Whenever this creature is dealt damage, put a +1/+1 counter on it." (It must survive the damage to get the counter.)

All Slivers have shroud. (They can't be the targets of spells or abilities.)

Akoum Refuge enters tapped.
When Akoum Refuge enters, you gain 1 life.
{T}: Add {B} or {R}.

Whenever a Sliver you control attacks, defending player loses 1 life.

Blooming Marsh enters tapped unless you control two or fewer other lands.
{T}: Add {B} or {G}.

All Slivers have "{T}: Regenerate target Sliver."

All Sliver creatures have flanking. (Whenever a creature without flanking blocks a Sliver, the blocking creature gets -1/-1 until end of turn.)