Mana Surge

(You may cast a legendary instant only if you control
a legendary creature or planeswalker.)
Switch your mana pool with target opponent's
mana pool. (All mana is removed from your mana
pool and put into target opponents mana pool. All of
that player's mana is removed from their mana pool
and put into yours.)
Zendikar was the perfect spot to chain the eldrazi, its
mana constantly shifting.