Magmatic Hollow

Creatures don't untap during their controller's untap step. At the beginning of each player's upkeep, untap all creatures he or she does not control. For each creature untapped this way, Magmatic Hollow deals 1 damage to that creature's controller.
"One does not walk through the hollows of Rhiia. Rather, one fights through them. All the while, one false step means a fiery fate."
-Grenka Jyn