Sliver Abomination

When Sliver Abomination enters the battlefield
or attacks, reveal the top X cards of your library,
where X is the number of slivers you control.
You may cast any number of sliver creatures
revealed this way with total converted mana cost
X or less without paying their mana costs. Put
the rest on the bottom of your library in any
order.
A mad wizard once attempted to breed the perfect
sliver. Unfortunately, she succeeded.