Eren Yeager, the Determined

Partner
Whenever a creature an opponent controls
enters the battlefield, put a +1/+1 counter on
Eren Yeager, the Determined.
{1}{g}: Regenerate Eren Yeager, the Determined.
At the beginning of your end step, if Eren Yeager,
the Determined has 6 or more +1/+1 counters,
transform it.