Avacyn angel

[ibtrickey]

What can you do if someone gets this out?? {Avacyn, Angel of Hope}

[Wally]

 {Oblivion Ring} or morbid  {Tragic Slip}
Make them sacrifice their stuff with  {Killing Wave}

[MementoMori]

 {Merciless Eviction}, {Terminus}

[Double-O-Scotch]

{swords to plowshares}, {clone}, {slave of bolas}, {condemn}, {pacifism}, {dispatch}, lots of stuff can deal with avacyn...

[Silent1236]

{All is Dust}!

[Trunksthemighty]

You cast your own  {Avacyn, Angel of Hope}

[All-Mana Mania]

Wait would the legends thing work? Since avacyn an all permanents you control are indestructible

[Double-O-Scotch]

Legend rule isn't a "destroy" effect, so yes, it would work.

[Rasser]

 {Clone}
{Phyrexian Metamorph}

[KILLERBEE]

KILL IT!!! KILL IT WITH FIRE!!!!

[Rass]

Steal it

[ibtrickey]

What if I am working with a standard green black deck myself??

[MementoMori]

The previously mentioned  {Killing Wave} and {Tragic Slip}, plus {Devour Flesh}, {Liliana of the Veil}, and {Mutilate} or {Liliana of the Dark Realms}'s -3 if you have enough swamps. I can't think of anything green can do about her.

[Rasser]

Also  {Death's Approach} or {Death Wind}  or  {Barter in Blood} 
{Helvault} could be used as well

[Wackaman9001]

Definitely use {helvault} if nothing else than the delicious flavor of removing her with her own prison