Altruistic Mammoth

When Altruistic Mammoth enters the battlefield,
sacrifice any number of lands you control and
then put a stomp counter on each land sacrificed
this way that is in your graveyard.
When Altruistic Mammoth dies, return all lands
with stomp counters on them from your
graveyard to the battlefield tapped.
{t}: Add X mana in any combination of colors,
where X is the amount of lands sacrificed with
Altruistic Mammoth, multiplied by two.