Shadow Ninja

Shadow Ninja can't be blocked.
When Shadow Ninja enters the battlefield,
choose any creature you control. Shadow Ninja's
power and toughness are always equal to that
creature's power and toughness. Shadow Ninja
can't attack or block, unless that creature does.
Whenever that creature becomes the target of a
spell or ability, target Shadow Ninja instead. If
that creature dies, sacrifice Shadow Ninja.