Thoros, Inner Demon

Bestow {x}{x}{b}(This card is an Aura until removed.)
X is enchanted creature's toughness. Bestowed non-enchantment creature gets a -1/-1 counter during its controller's upkeep, then deals X damage to its controller. If cast as a creature, put any amount of -1/-1 counters on Thoros.
For each counter on Thoros, or the enchanted creature, Thoros gains your choice of Flying, First Strike, Trample, Deathtouch, or Prowess.
{x}{b}: Thoros detaches and deals X damage to the bestowed. Any player