Still Waters

At the beginning of your upkeep, you may
tap target creature you control until the end
of the turn. If you do, tap target creature
that you don't control until the end of the
turn. This ability only triggers once.
"They say that Still's boat sits in a place where the
waters never stir. Any who have dared to try and
find him had to sacrifice everything that would stir the waters. Everything." Crazy Old Willy.