Zeromutarts Challenge-5 (encodings)

Website :http://zeromutarts.de/

Question :
I believe a flag is hidden in this encoding. Can you find it?:

TWF5YmUgeW91IHNob3VsZCB0aGluayB0aGUgb3RoZXIgd2F5OiBbKSJ9cmdoZW9faGdfZ3J7dG55cyIgOnJmbnBlcmpieSBhdiB0bnlzIHJ1ZyBnYnQgaGJMIC9iXCAhcnB2QSggOj90aSB0ZmlocyBuZXZlIHVveSBuYWMgLHJhZW4gc2kgZG5FIG5BXQ==

Fine , First thing to observe is "==" in the message ..Its a base-64 encoding is what can be concluded..

Base-64 online tool

we get :
Maybe you should think the other way: [)"}rgheo_hg_gr{tnys" :rfnperjby av tnys rug gbt hbL /b\ !rpvA( :?ti tfihs neve uoy nac ,raen si dnE nA]

After reversing we get : 
An End is near, can you even shift it?: (Avpr! \\b/ Lbh tbg gur synt va ybjrepnfr: "synt{rg_gh_oehgr}")

After shifting 13 times that is 'M' is the key..
we get :
Na raq vf arne, pna lbh rira fuvsg vg? : )Nice! \o/ You got the flag lowercase: "flag{et_tu_brute}")]

Flag : et_tu_brute