The Ring

At the begining of your end step, put a Darkness counter on equipped creature. Equipped creature
has -1/-1 for every Darkness counter on it.
{t}: Equipped creature phases out.
{b}{b}{b}{b}{2}: If equipped creature has at least 4 Darkness counters , it becomes a 10/10 Demon
and has Indestructible, Trample and Hexproof.
Remove all Darkness counters on it.
Equip {b}{b}{r}