Gruul charm vs Mutavault

[SoshiGanrou]

Ok so I think I know the answer but just want to clarify and make sure it's right. So I have mutavault and a assemble the legion token on my field. Mutavault is still in land form. My opponent casts gruul charm to make my guy not able to block and get in for the last point of damage. I let the charm resolve and at the end of attack step I animate mutavault so it can block. He said it doesn't work. I say it does because mutavault wasn't a creature he wouldn't be affected by the gruul charm. It affects the current board and anything after is not affected. Is that correct?

[Steerpike]

{Mutavault}
{Gruul Charm}
{Assemble the Legion}

[Kaleo42]

1/24/2013   If you choose the first mode, no creature without flying will be able to block that turn, including creatures that lose flying and creatures without flying that enter the battlefield after Gruul Charm resolves.

[AkiraDeLaine]

Gruul charm says it works until end of turn, turn isn't over at declaring blockers

[Kaleo42]

Gruul charm says it works until end of turn, turn isn't over at declaring blockers

His question is base on whether it effects the creatures in play or creatures in general. As the ruling I posted says it does effect all creatures that exist within that turn.