No...that's sort of exactly what is printed on the card.
The End Step is a Step.
May 24, 2014 9:09 p.m.
No, it doesn't. As the card says, it doesn't empty at the end of any step or phase. This includes the Clean-up step.
It basically stays there indefinitely as long as he's on the battlefield.
May 24, 2014 9:11 p.m.
Or until it is used? My mate seems to think that he can tap 4 green, play a four drop and omnath is still a 5/5.
May 24, 2014 9:42 p.m.
If you spend mana, it isn't in your mana pool anymore...