Slenderman, The Final Thought

No player controls Slenderman.
At the end of each upkeep, Slenderman
gains control of a creature he doesn't control with
the lowest power chosen at random.
At the beginning of each attack step, untap all creatures Slenderman controls and put a
-1/-1 counter on them. Those creatures attack
their owners if able.
{2}, Discard a card: Gain control of target creature
you own. Any player may activate this
ability.