The Nightwatcher

This creature may not be bonded with a legendary creature. When The Nightwatcher is bonded with another creature choose one: Double
the bonded creature's power and toughness, but it
may no longer cast spells or reduce the creature to
0/1 but activated abilities are doubled.

Soulbond (you may pair this creature with another unpaired creature when ether enters the battlefield they remain paired as long as you control them both.)