Sliver Hive

{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to cast a Sliver spell.
{5}, {T}: Create a 1/1 colorless Sliver creature token. Activate only if you control a Sliver.

Secret Lair Drop

Jumpstart: Historic Horizons

Magic 2015

{T}: Add {1} to your mana pool.
{T}: Add one mana of any color to your mana pool. Spend this mana only to cast a Sliver spell.
{5}, {T}: Put a 1/1 colorless Sliver creature token onto the battlefield. Activate this ability only if you control a Sliver.

Whether you control a Sliver is checked only when you activate the last ability, not as that ability resolves. If you control no Slivers at the time the ability resolves, you’ll still get a Sliver token.