Tara, Sliver Terminator

Firststrike, Reach
You get {e} whenever a Sliver creature enters the battlefield.
When Tara, Sliver Terminator enters the battlefield, get one {e} for each Sliver creature on the battlefield.
Tara, Sliver Terminator's power is equal to the number of energy counters you have.
"I want to change the future, that is why I am here. The Slivers don't belong on this world." - Tara, Sliver Terminator