Omnath, locus of void

whenever another spell or permanent would add colorless mana to
a mana pool, add twice as much mana instead.
Colorless mana doesn't empty from manapools as
turns or phases end.
Omnath has +X/+X where X is the amount of colorless mana in your manapool divided by two.
as the world Omnath was formed from died, so did he.