Coalition Sliver

Banding
Other Sliver Creatures have "Bands with other
Non Legendary Sliver Creatures."
On your turn before defenders are declared,
whenever 3 or more Sliver Creatures you control are
in an Attacking Band, each Non Token Sliver in
that band get +1/+0 for every other Sliver in that
Band until End of Turn and +0/+1 for every
creature target opponent controls until End of Turn.