Do I need to defeat the elite 4 for 2nd time to access the cave with meow (last legendary bird)
there a man blocking in the entrance...
I beat the elite 4 but dont have yet a legendary dog.

First off whos meow and what the heck is he and if you mean Mewtwo and yes you have to beat the elite 4 two times to get him and get the national dex.

If you've beaten the elite four and you can't find your legendary dog then you should LOOK AROUND!!!!! Makes sense doesn't it??? I mean that's how you find every other flippin pokemon isn't it???!!! And Meowte is not real, neither is Mewthree if that's meant.

I think that i have made MY POINT!!!!!

quote rmr1976

Do I need to defeat the elite 4 for 2nd time to access the cave with meow (last legendary bird)
there a man blocking in the entrance...
I beat the elite 4 but dont have yet a legendary dog.

Meow? There are only 3 legendary birds and Meow isn't one of them... If you're talking about Mewtwo, you need to retrieve the Ruby and the Sapphire before you can enter Cerulean Cave (where you catch Mewtwo).

Yeah and you only get the legendary dog at random while walking around in the grass. Your not going to just have it once you beat the elite 4.

Lets make it clear here are the following pokemons and there locations and way to catch
1. Articuno: Seafoam islands use boulders to change the flow of water and go up to catch it
2. Zapdos: Go to the power plant keep on going north unless u find Zapdos
3. Moltres. Found in Mt. Ember have to move the boulders to reach it
4. Mewtwo: Found in cerulean cave have to defeat the first wave Elite four and second wave elite four (after Sevii islands)
5. Mew : either use a heating device or go to a nitendo event for mew
6. Lugia :either use a heating device or go to a nitendo event for lugia
7. HO-OH :either use a heating device or go to a nitendo event for HO-OH
8. Deoxys :either use a heating device or go to a nitendo event for Deoxys
9. Jirachi :either use a heating device or go to a nitendo event for jirachi
10. Any Dog (Suicune,Raikou, Entei) : RAndom in wild use Crobat ( mean look) or Dugtrio ( arena trap) to prevent them from fleeing use master ball on them if u dont wanna use any of the above given suggestions

THIS HAS TO CLERIFY U