Commander O'Niall

When Commander O'Niall enters the battlefield,
create a 2/2 white knight creature token with
vigilance.
Whenever Commander O'Niall attacks, you may
exert him. If you do, create a 2/2 white knight
creature token with vigilance.
Whenever another knight you control dies, put a
+1/+1 counter on Commander O'Niall.

Just kill them both quickly.