Poisonous Canyon

When Poisonous Canyon enters the battlefield,
each player gets 3 poison counters.
Double Tap (If this permanent is tapped, you may
tap it an additional time, making it double tapped. If
this permanent would untap, it becomes tapped.)
{t}: Add {u},{b}, or {g} to your mana pool.
{u}{b}{g}, {t}: Add {4} to your mana pool.
{4}, {t}: Until end of turn, players may spend
poison counters as though they were life to cast
spells.