Rintar, Sleeper Agent

Rintar, Sleeper Agent enters the battlefield under target opponents control with three phyresis
counters on it.
At the beginning of Rintar's owner's upkeep, they remove a phyresis counter from Rintar and put
one on another target creature. Then, if Rintar
has no phyresis counters on it, it's owner gains
control of it.
{2}{b}: Gain control of target creature with a
phyresis counter on it. Only Rintar's owner may activate this ability.