Tishdeth, Blade of Chaos

Whenever Tishdeth, Blade of Chaos attacks,
roll a d20.
1-10 | Place a +1/+1 counter on each Tiefling
and/or Demon you control. Place an additional
+1/+1 counter if that creature is attacking.
11-20 | Place a -1/-1 counter on each creature defending player controls. Place an additional
-1/-1 counter if that creature has a +1/+1
counter on it.